I need to know how to make variables from certain things. I'm not talking about $game_variables either.

I have my 'input' screen, where the user can input a number, the variable is called @deposit_number. I don't know how to make it so that the deposit number is added to a storage number, such as @amount. I think it's:
@amount += @deposit_number

But, I haven't actually made @amount yet; so that is first thing to do.

Thanks for any help

edit: typo