what are groups that I can join?

look under the forums Category "Group Recruitment".
there you can look for groups you can join. they usually post their requirements (e.g. lvl, ratio, making regular GAs inside the group, ...). if you meet them, you can ask to join.
but be aware that not all of them are open for new members at all times

recommendations:
Unlucky7, for new SG members that have less than 7 wins
PAGYWOSG - Play a game you won on steamgifts, youre supposed to play won games there that fit a monthly theme. its also possible to participate with backlog games if non of your wins fit the theme. please read the rules first though
Playing Appreciated, win a game and play it within a month, sounds simple? then you can join, just read the rules

As AiKirika mentioned Unlucky 7 is one I recommend as well. It's designed for new members of SG like yourself as well as people who haven't had 7 wins yet.

One of the most important things you should do before you join a group though is make sure you understand the rules here on SG. You should read the guidelines as well as the FAQ. Understanding these things will help make sure you don't run into any issues.

Then if you've done that then when you go to the group recruitment threads on the discussion boards you should always read the rules of the group itself before you apply/join. A lot of the groups have requirements for example, making at least 1 giveaway a month, giveaway ratios, playing the game you won etc.

If you aren't understanding something you can always submit a ticket to our support team and we'll do our best to help. We also have a lot of helpful people here in the community that I'm sure could answer your questions as well if you're confused about something that you've read in the guidelines or FAQ.

but why u made a ga of a game you won here?

You're gonna want to fix that error you made with your first giveaway. That's gonna help.