The bio sculpture course (yes, good brand, so is Shellac but they're different things) will teach you to extend using gel (a stronger, builder gel, as opposed to a gel polish (which doesn't give strength really just lasting colour & shine). So after the bio course you'd be able to offer nail extensions if that's what you want, whereas with gel polish you can't make the nail longer.
Other extension courses that are good are also run by Nail Harmony, Nsi, CND and more. You can extend with either tips or by sculpting (using a form as a platform to build instead of a tip) and obv bio-sculpture falls into that camp (hence the name)
If you're not bothered about extending but want to use gel-polish then there are lots of decent brands as you'll see from threads on this site, I use CND Shellac but a lot of geeks on here swear by Gelish, Ink London, OPI gel colour, etc. I'm sure others will advise you on their favourite or you can do a search on here. Personally I'd go for somewhere that asks you to produce your certificates before they'll sell to you
Sorry for all the waffle, hope it makes sense lol.
Was your course generic or with a particular brand? And was it gel (extensions) or gel-polish)?