Hello and welcome to Steem!

I would recommend going to your Wallet-page and power up the Steem you have, as the Resource Credits you have to use are based on the Steem Power.
Steem and Steem Power are kind of the same, but Steem Power is "locked" as power on your account giving you more resource credits. The resource credits are limited for different reasons including to prevent spam from small power accounts.

Just in case you don't have enough RC to power up right now, I'll also borrow some SP to you.

If you have any questions to ask, just leave a comment or find me on the chat :)