One of the first orders of business in For Honor is to unlock each of the nine classes. To do this you will need to collect steel, which isn't earned so easily. However there is one simple way to get a sizable chunk at the beginning of your journey.
The first thing you should do is complete the tutorial. The basic and advanced tutorials will reward you with 3,500 steel. With this, you can purchase seven of the classes.
From here, the best thing to do is to play Dominion in multiplayer. Do your best to be successful with your team, and you will find yourself with plenty of steel for buying the final two classes.