The player can be controlled with WASD, while the mouse is used to aim at enemies at shoot them with your primary and some secondary weapons, Left mouse button for Primary Weapon usage and Right mouse button for Secondary Weapon usage, you can cycle between your Primary Weapons with numbers 1 - 9, 0 is for the Cannon slot which is the last Primary Weapon you'll obtain, you can also cycle between your Primary Weapons right the Right CTRL button and the mouse scrolling wheel, for Secondary Weapon you can cycle with Z, X, C, V, B, N, this corresponds to the your Secondary Weapon slot, like Z for Mines and X for Spider Mine, you can also use the Tab button to cycle for Secondary Weapons as well.
To control the tractor once again you will use WASD but controlling it properly can be a little tricky, always do note that W is always the Forward button and S will be the Backward button, while A and D is for turning your tractor around, the front of the tractor is like a bumper and this is what you should remember when controlling the tractor, the W button will always go forward to where the tractor and its bumper is facing, and the A and D will turn it around to left or right, you will be rarely using S, sometimes not at all.