Right from the get-go, Iron Marines would toss you to the missions to give you somewhat of a practical crash-course. As you go along and progress in the early stages of the game, every time you encounter a new unit, enemy, structures and elements, you'll be given a notification icon on the right part side of your screen. Once you see these icons pop out, you may click on it (will automatically pause the game) and view information regarding that particular new element that you have just encountered in the game.
For a casual gamer, this game is not as easy to play compared to your typical tower defense game or even the usual likes of mobile-app-based RTS games. Surprisingly though, the tutorial leg of this game makes it easy for players (even complete beginners) to get a good grasp of how to play it without overwhelming players with the complexities of all the elements present in the game. Even if for instance you may have encountered something new in the game, it gives you the chance to check on it whenever the chance permits you.
The neat thing about learning how to play this game is that almost everything has info in it before you get to actually even access the thing that you are interested in. At the chance you wish to continue your action, you'll always have to press on the check mark to give it a "go". This is rather helpful especially in introducing every element present in the game.
The basic make-up of the tutorial part of the game basically teaches you how to control the different units individually and/or collectively. This will be integrated with the Introduction of the different units, installations, and heroes, in the first few levels of the game (stages 1-3). This tackles the scope and limits of enlisting units, their basic differences, and how to properly utilize them in different situations.