QUESTION Which study fits the best?

[cysoon]

Hello,

I'm using GetSimple at my work for the company website. I didn't install it but my collegue who has left the company. In one day he told me something about GetSimple CMS...
The website need to be updated and some new products to be added.
Before going in it I was wondering what would be good to do?
I mean; I do know something about html and css, but I want to do a study.
When I'm right GetSimple generated a html website with his CMS?
So a study about html will be the best choice or html5 or ?
I hope I'm clear if not let me know and I'm looking forward to the comments.
Thanks in advance!