Really, it isn't all that hard. It's not like you're in charge of finding the Higgs boson in the Large Hadron Collider.
It's not as easy, though, as you seem to think. Depending on how you think you might stumble on the fine points of a theory and become confused. Then it can be only a matter of time before it all comes tumbling down. In the recent -ing thread, you linked to OWL Purdue on participles. I'm now going to pick apart that link and analyse the potential problems with their approach. You may say it's nitpicking, but it's not. People who honestly think things through may fail to make sense of the entire system
because of these niceties. They're real, and they have led notable grammars to abandon the distinction between gerunds and participles (most recently, I think the
Cambridge Grammar of the English Language).
As a reminder, the links:
Participles
Gerunds: http://owl.english.purdue.edu/owl/resource/627/01/
OWL said:
A participle is a verbal that is used as an adjective and most often ends in -ing or -ed. The term verbal indicates that a participle, like the other two kinds of verbals, is based on a verb and therefore expresses action or a state of being.
***
A gerund is a verbal that ends in -ing and functions as a noun. The term verbal indicates that a gerund, like the other two kinds of verbals, is based on a verb and therefore expresses action or a state of being.
So what a participle and gerund have in common is that they're verbals. They are based on a verb, and we know this because it expresses an "action or a state of being". A participle functions as a an adjective, and a gerund functions as a noun:
However, since they [participles] function as adjectives, participles modify nouns or pronouns.
***
However, since a gerund functions as a noun, it occupies some positions in a sentence that a noun ordinarily would, for example: subject, direct object, subject complement, and object of preposition.
Now this is interesting: On their
parts of speech page they say that a "noun is a word that denotes a person, place, or thing." This is different from what they say above. This is not a surprise, since they say "gerunds" are verbals and they
function like nouns. That is: they're not nouns, but they take their place.
However, compare what they say about adjectives on their parts-of-speech base: "An adjective is a word that modifies, or describes, a noun or pronoun. Adjectives may precede nouns, or they may appear after a form of the reflexive verb to be (am, are, is, was, etc.)." This is pretty much the same as what they say that "participles" do.
The conclusion? They define nouns and verbs according to what they refer to (semantic definition), but they define adjectives as what they do in a sentence (functional definition). This is confusing and inconsistent. Traditional grammar has this problem.
Let's go back a bit:
Creamation in "Grandpa's cremation" is a noun. "Cremating Grandpa" is a verbal (let's not talk about the distinction between pariticples and gerunds at that point). That means that, according to the definition "cremation" is a thing, and "cremating" is process. But what
is that distinction? We're certainly referring to the same real-life object, but in different ways. This may be intuitive for some people; it never was for me, and there are certainly others who don't like that, either.
So how does this work out? This gets more complicated as we read on: we find that it is the pariticiple phrase that functions an adjective: So in "Removing his coat, Jack rushed to the river," it's "Removing his coat" that functions as an adjective, rather than only "removing". But that transfers the definition of the participle as modifying the noun to the phrase and leaves you hanging. The same phrase could be a gerund: "Removing his coat was not easy for Jack." So what do we do with "removing" when all we have is "removing his coat"? We have not enough information to differentiate between gerund and participle, because it's decontextualised. And that means that "participle/gerund" are sentence functions and not word classes, here. Is there another way to interpret this?
Still, what do I make of the definition that the participle is a verbal that functions as an adjective? Did they lie? Did they mean to say that it is a verbal that occurs in a phrase that functions as an adjective? Were they
careless? Also couldn't we say that "removing" in "removing his coat" functions like a verb regardless of context? You know, because it takes an object? Maybe, maybe not. This is a can of worms I'm
not going to open here.
All of this can be inconsequential. Generations of grammarians had no problems with it. But more structural thinkers (and I'm one) do have severe problems with that. It's confusing.
Fine, what's next: Oh, yeah: What's the evidence that
"Removing his coat" in "Removing his coat, Jack rushed to the river," is actually modifying "Jack", as they claim? What if I claim that it's an adverbial that gives us the manner in which Jack rushed to the River? Is this based on semantic plausibility? What about this sentence:
Jack having removed his coat, I walked away.
This is sort of similar to the above, except that the subject of the verb is no longer implied, but explicitly expressed. Does "having removed his coat" now modify "Jack", even though it looks a lot like a subject? Huh? Does the entire phrase now modify "I"? I doubt it. But wait. Phrase? If "Jack" is now a subject, is this maybe not a phrase at all, but a clause?
If so what, exactly, is the difference between a phrase and a clause? And how does that figure into the entire discussion? Do I have to decide whether something is a phrase or a clause before I can even tell as what it functions which is necessary for determining what kind of verbal it is in the first place?
I'm going to stop here. People have probably stopped paying attention by now, anyway. The thing is that what sounds easy and simple isn't necessarily easy and simple. If that mess makes intuitive sense to you, you're lucky. It never did to me. I went through school without understanding the difference between adverbs and prepositions. Had to go to university to find out.
Sure, few people will have problems to identify the nouns and verbs in sentences like:
The
cat
sat (v.) on the
mat 
.
But who knows what that looks like if you lose the plot, or if it never made sense in the first place. Please, please, please don't assume things are easy because it makes sense to you. Sure, it's simple. And answering tests correctly doesn't seem that hard, either (mrsvalkyrie says she aced English, after all). But, you know, if that sort of stuff makes no sense to someone they're not necessarily stupid. It's possible that they're looking at it from a different angle than you. Or that they're seeing problems you're unaware of.
Snake oil salesmen these days sell books grammar. Beware. (And, no, the OWL folks are
not sanke oil salesmen. They know what they're talking about; they're just simplifying and try to gloss over the diffucult stuff that would only confuse their students. But some students notice that stuff anyway, and in that case...)
I'm sorry if this all confusing and makes things worse rather than better, but I don't really like it when people make things more simple than they are and then use that to make others feel stupid. It
is complex. The reason that few people actually get confused by that sort of thinking is exactly because it's entirely unnecessary to know this sort of theory stuff to use language. So, yeah, if you're interested you're welcome to think this through. If you're not, just guess what the people in power want to hear and go with that (whether it makes sense or not). And don't feel bad for not getting it. It's really not as simple as everyone says.