How does someone join a clique at school?

I'm a guy i'm 17 and I have social anxiety. I'm not part of any social group, so I used to sit alone at lunch break but that was giving me bad anxiety so now I just go home. I have 2 friends and a few acquaintances, but I'm not part of any social group even though my 2 friends are. I don't know how people join them. People join cliques by forcefully ingraining themselves into the group.

Example:

Student #1: "So anyways I was playing Minecraft-"
Student #2: "DID SOMEONE SAY MINECRAFT?!"
*Student #2 poofs over the Student #1's group and makes himself part of the conversation, all because he found the right opportunity to but in.*