Most US cities have buses, and big cities also have trains (called the subway, metro, light rail or commuter rail). Each city has its own transit agency with its own rules. You can find your city's agency under In your state.
Most systems accept one or more of these:
Transit card: a plastic card you load with money or a pass. You buy it at a machine in a station, at some stores, or online. Then you tap it on the reader.
Tap-to-pay: in many cities you can tap your contactless bank card or phone wallet (Apple Pay, Google Pay) on the reader. A small wave symbol on the reader shows it works.
Agency app: you buy a ticket in the app and show it to the driver or scan it.
Cash: many buses take cash, but the driver usually cannot give change. Bring the exact amount.
A pass (day, week or month) costs one price for unlimited rides. If you ride twice a day, it is often cheaper. Some systems give fare capping: when your taps reach the price of a pass, the rest of your rides that day or week are free.
Transit agencies that receive federal money must offer half fare at off-peak times to people aged 65 and older, people with disabilities, and Medicare cardholders.
Many cities also have discounts for students, children and people with low income. You usually apply once with proof.
Ask your school or employer: some give free or cheaper transit passes.
Find the bus stop sign with your bus number on it.
When your bus comes, check the sign on the front. Wave if the driver might not see you.
Get on at the front door. Pay or tap.
Before your stop, pull the cord or press the red STOP button. A "Stop Requested" sign lights up. If nobody asks, the bus may not stop.
Get off at the back door when you can.
Lines usually have a color or a letter, like the Blue Line or the A train.
Every platform shows the direction, usually by the last station ("Northbound" or "to Airport"). Check it before you go down the stairs.
In some systems you tap when you enter and again when you leave. Keep your card until you exit.
Stand back from the platform edge. Let people get off first.
Not having proof of payment. On some trains an inspector checks tickets and can give a fine.
Taking the seats at the front of the bus marked for older people and people with disabilities. Offer them if someone needs them.
Missing the last ride. Check the schedule for nights and weekends.