Telagram.. What?

Okay so I've been constantly hearing people talking about blackhat groups and interesting groups on telegram (i even hard about hacking groups) and it got me interested. So i downloaded and installed even on my desktop but it seems just like a messenger to me. My question is, how do i explore telegram more and be able to join some interesting groups? As I see groups aren't listed there.

i'm a complete noob on this so I apologize for the lack of knowledge but maybe it could also help me with my journey. thanks a lot!

People make groups which you can join.
Normally they have a link to that group. Then you join it and can post.

It's just like other messengers that support groups. You need a link to that group... Or try using the search bar at the top left (it's not only for searching your own history, but the whole telegram community), above your contact list.

Search your interested group on https://telegramchannels.me