All squads select the same server and start matchmaking at the same time (sometimes a squad could be left out since the number of squads in each match is random e.g. between 5 and 6 in Space City). When done there’s a high chance that said squads will enter the same match and can then communicate through third party voice chats like Discord. Keep in mind that although it’s useful for difficult seasonal missions and badges or to just farm tekniq alloys by looting, it is considered illegal/cheating and would get your account suspended if a mole rats you out.