Where can I exchange foreign coins and bills for American cash? [closed]

As a general rule, you can't - at least not outside of the country the coins are from.

Money changers, as a rule, will only accept notes for foreign currencies (and sometimes even notes above a certain value for some countries).

Your options are to either keep the coins until you travel back to the country they are from, or donate them to one of the many charities that will accept then - although even that could be difficult as they normally only accept such donations through either locations in airports (or international train stations), or though airlines.

One example of such a charity is the UNICEF Change for Good program. As per that page they will accept donations via mail in the US at least, but given the cost of postage it's likely not viable.