You may have to ask "Who do I make the check out to?" if you're not sure what to write in that line.
Note that it's a very bad idea to make a check payable to "cash". While this may be convenient for you, it's also convenient for anybody who wants to steal your money. If you're not sure who to make a check payable to, just hold onto it and don't sign it until you have the payee's name.
- See Pay to Cash for more details
Do You Even Need to Write Checks?