Free at home rapid tests are no longer available through the federal program. If you have private medical insurance, your insurer is required to reimburse you for rapid tests you purchase up to 8 a month.
The CDC has designed a quarantine/isolation calculator. It can be found here.
Regardless of vaccination status:
If you have tested positive, you must quarantine/isolate for 5 full days, and continue to wear a mask for 5 additional days when around others.
If you have been exposed, within 6 feet for at least 15 minutes total, you must wear a mask for a full 10 days when around others. You no longer need to quarantine.