reason being that I have come across some other websites as well that have bitcoin in their names like "bitcointalk", but all they do is advice you to invest with them.
There's a significant difference — Bitcointalk doesn't sell you anything. It's just an online forum where people talk about bitcoin/cryptocurrencies.
that's true, but I suggest to OP to be cautious, the forum is riddled with scammers. don't be afraid to ask if you have questions regarding a certain project or about the credibility of a user you want to transact with.
also, just to add to what mk4 shared, I suggest reading this thread too "
Newbies - Read before posting" it is a very useful thread for users that are new to the forum