RC stands for Resource Credits . It is required for everything that you do on Hive blockchain , if you want to post , comment , vote etc it takes RC .

How do you increase them ? by staking Hive ( or in other words power up your Hive ) . The more Hive power you have the more RC you get and hence the more transactions that you can perform on Hive .

Where can you see your RC ? - https://hiveblocks.com/@ceestitches