They do quarterly or bi-annual statements, those statements will have the checks if it passed your advance amount. If say you had a 5k advance, you have to make that much in royalties before you see a check.
After that it will show up with your statement that will show you how many books are sold. There will be some sales that are reserved as returns for up to a year, those are books that bookstores purchased but may not have actually sold yet, and they may later return them or exchange them for other books so that would come back off your sales.