Yeah no worries man. The 'mana' is a reference to the Steem credit system.
Basically because everything you do on the Steem Blockchain (opening an account, leaving a comment, uploading a video, upvoting, etc) is a transaction that incurs a real-world cost, which is paid by the Steem mining community.

Each block that gets put on the Blockchain (every transaction) must be mined by someone, and doing that requires you to have a dedicated machine that is almost always turned on - which obviously costs money to do.

The 'mana' aka, the credit system exists to limit the number of transactions you can make at any given time, as to not overload and congest the network.

Btw, the amount of credits allotted to you is effected by how much Steem Power you have. The more Steem Power, the more credits. The more credits, the more comments and upvotes and uploads you can do in a given time frame (usually 2-4 days).

Anyways, your ability to comment and upvote will grow as your author rewards and curation rewards start awarding you Steem and Steem Power.

Anyways, sorry to ramble - I say all of this because I know I wish I had someone explain it to me when I started. lol.