You will learn a LOT from installing and configuring a zencart site.

Firstly... flat HTML is "old school" for websites. If you intend making a career out of site building and coding, then you will need to learn how modern CMS platforms operate - and there is no better way to do this than to use a good OpenSource system.

While there are a few "patchy" solutions to adding eComm to a flat HTML site, none are regarded as safe, reliable or professional.

Again, if your objective is to learn how CMS sites work, then load up zencart and have a go at configuring it.