As far as I understand, once you've used your RAM to make a transfer you don't get it back.. I believe this is because RAM is used when you need to store your transaction on the blockchain. The EOS system has RAM available for purchase which fluctuates based on the Bancor Relay algorithm which is based on supply and demand. DAPPS obviously require lots of RAM because they will be required to store more information than users. You are also able to sell RAM for tokens and buy more when you need it.

Hope this helps, if anyone else has suggestions please inform us! I'm still getting into it.