American Contract Bridge League: https://www.acbl.org. Membership is only $5 per year for juniors 25 years old and younger. The membership fee can be reimbursed by the club.
Bridge Base Online: https://www.bridgebase.com/. Play bridge online.
Draper Lab Bridge Club: https://web.mit.edu/mitdlbc/www/. Matches start on Tuesdays at 6:30pm in room 2-131. Earn ACBL masterpoints.
For learning: