Welcome to MA!
We have a Guide section here that can get you started off,
MA GuidesReading the Reference Guide on the units and their intended counters posted by Immortals is always a good first stop at learning the game,
WOL Reference Guide: T1-4 Merc stats and countersas well as one for the heroes of MA,
WOL Reference Guide: Hero stats and upgradesWe have some members who have been gracious enough to put together some youtube videos which you can find here,
Marine Arena Youtube Videos - if you click the link button on the far right it will take you to their channel page listing all of their videos.
You can also search around youtube for past/present tutorials,
Youtube MAYou can also download and watch the many replays posted in this very section by the members of this forum to learn how they play and the strategies they use.
MA-WoL Strategy / Replays / Streams as well as the replays from past MA tournaments
MA US-3MA US-4MA US-5MA US-6MA US-7As well at any time ask in this section of these forums advice on any specific strategy using the units and dealing with their counters.
Good luck and hope you enjoy Marine Arena as much as we do!