Most classes don't require you to bring a partner. Usually the females rotate (or the men can) so everyone has a different partner each time. Even if you brought a male friend, you would still have to rotate so you each get a chance to dance with different people. This is important so you get a better understanding of your role as lead or follow, because everyone dances differently and it helps you to adapt and become a better dancer.
What tango are you interested in, Argentine or American? I'm decent in American but Argentine scares me off (so intimate!), lol. Good luck and have fun!!