It's called a "cash" coin. Your best bet is to find a book or website to get info on them because they've been in use from B.C. all the way up to the 1900s. You'll be able to identify it by the different characters on it.
Well now...if the pictures of the coins are any indication of mine...my coin appears to have been minted/used from AD 1736-1795-Emperor KAO TSUNG...very neat find...