To progress in the game of Mech Crusaders, you will need Experience. Experience is gained primarily via the Battle Arena, by pitting your team of mechs against that of another commander in battle, and winning. Another way to gain experience is via the Plains, but at a much decreased rate.
When you fight in the Battle Arena, your mechs will gain Experience which will cause them to level up and provide you with Circuits to improve their health, skills, and damage resistance and wires to refix the power levels of the Circuits.
Mechs need experience to level up and grow; the same is true of your commander. As you gain experience, you level up, which gives you access to many new Commander Skills (abilites that allow you to use more mechs in the Arena, increase your mining gains, increase your equipment upgrading skills, etc.), and the ability to purchase new and better mechs in the Mech Shop and equipment from The Armorers to use. Note that even if you lose a fight in the Battle Arena, you still gain a little amount of Commander Experience.