OK, I'm new so how exactly trading works here? Couldn't find the info in the first post.
I bought couple games that I tried and they turned to be not my cup of tea, so it would be nice if I could trade them for something I might actually play. But I couldn't find anything about trading here except buying a game as a gift and sending the code to someone and expecting him to do the same. Is that how trading works (i.e. I'm stuck with those 2 games I'll never play), is it a Galaxy only feature (haven't tried Galaxy yet) or is it a feature not available for new members?
Sadly you're stuck with the 2 games. Once a game has been redeemed to an account they're yours; you're not legally allowed to trade them.
When people on here trade they're usually trading extra copies of games where the serial hasn't been redeemed or they have gift copies provided on other sites like Steam. These occur in a number of ways... lots of people buy Humble Bundles for example: http://www.humblebundle.com
/ or me for instance... I just traded away an extra copy of Neverwinter Nights the other day. I had an extra serial number provided by GOG from pre-ordering the Witcher 3 on here... a game that's so old that even with out it being in bundles I own 2 or 3 copies of it. (I think it's 3... 1 disc based, 2 digital).
There's no rule about new members not trading but lots of new accounts are actually scammers trying to steal games (because they're losers most likely) so you'll have a hard time trading than others. The best advice is to be active & interact with other people for some time. That said anyone who does trade with you will likely ask you to send your game 1st... however lots of scammers will do this as well.
As for the games you bought & don't like... best bet is to try & get a refund from GOG. There's a chance they'll allow it but the official refund policy is here: https://www.gog.com/support/website_help/money_back_guarantee