MTGO is a strange game for me because it's seasonal. I don't know if I've ever played a computer game so strongly seasonal. There's a best time to play it and times when playing it is economically challenging. I mean, you can play it but it costs more, you get beaten more and the thrill of novelty isn't there.
Here's how the game works and how I approach it. A new set is issued about 4 times a year. The set is available in physical form only over a weekend known as the Pre-Release weekend. Then the game is released online on the Monday.
That Monday and the days immediately after the game is full of casuals who only return at this particular time in the cycle as well as both casuals and veterans who don't know what the new cards do. In addition many of the new cards are highly sought after by people who play constructed.
These conditions (mediocre players and high card prices) degrade rapidly, hourly, and then continue to degrade more slowly over the life of a format. The people who are playing in a format's final week will tend to be the most dedicated players.
MTGO is an expensive game with that expense defrayed by prizes. Many formats also allow you to keep the cards you open which is another way to defray costs. It is a very good game, better than Hearthstone, because you can dick with the other player during their turn (or anticipate them dicking with you and trump them). It' can be supremely satisfying.
Players have a concept of Expected Value which is calculated from your win rate. This calculator allows us to work out whether we're likely to be ahead or behind.
A big part of mastering the economics is selecting the format. Draft tends to have stronger players than Sealed, Competitive tends to have stronger players than Friendly. I play Friendly Sealed which not only has the weakest players but also has the best EV at 50% per the calculator.
I'm a decent but not great MTG player. (Limited Rating 1708). By stacking the odds I'm able to come out ahead (known in the community as "going infinite").
Here's how I finished my last league, a set of Sealed games I went 6-3.
I'd very much recommend playing limited format MTGO and I hope this helps some of you find your feet. Beginner's guides are on the sidebar of the MTGO subreddit.
The next Limited format starts in January so now would be a good time to pootle around for a couple of months learning the UI and the game mechanics and play some beginner games to prepare yourself for then.