simple selling via your website

You either do it manually (which is a PITA) or you invest in store software (which is either expensive, or very glitchy). And you take on all the liability of handling people's transaction related info, or you try and get them to mail checks.

Overall. PITA.

I did think about selling from my own web site and my conclusion was ... To have a website that is able to deliver files , in a number of formats , and take secure payment for them is not easily done . You will also need to attract customers . Unless you are a successful author, it is probably better to sell books via third party sites . If you would like to test the waters , and you don't mind giving your book away for free . You can submit stories Here
https://feedbooks.zendesk.com
it is useful to promote your work and gives a introduction to the process of submitting e-book

You can get an Amazon link that automatically sends them to the right sight for their country. Not everyone uses amazon but a lot do.

In Wordpress there are plugins for selling media. I just googled 'wordpress sell media plugin'

The normal approach is they connect to PayPal to collect the funds so you need a PayPal account.

I have no personal experience with it, but gumroad.com is supposed to be a fairly simple storefront that other self-publishers are using on their sites.