If I was subcontracting work from another person and he refused to pay me, what can I do?

You sue him--that's the best way to recover your funds.

A contract is enforceable, such as a contract to perform certain work or provide certain services in exchange for certain payment or compensation. The agreement is enforceable even if its an oral (sometimes incorrectly called verbal) agreement, though, of course, there can be some practical difficulties in proving the tems or even existence of an oral agreement.

So, to recover your money, you sue the person who's failed to pay you; you will need to prove the terms of the agreement, that you did the work, and what you should be paid. For smaller amounts, you can act as your own lawyer in small claims court; for larger ones, hire an attorney.