It is a lot to learn at first and can seem very daunting. However, once you learn how each part works and interacts with the others it becomes pretty easy and fun to put things together.

If you only need to drive two motors to control the two driven wheels then you'll only use two of the six channels you have available. You can assign each channel to a stick axis on the TX or use mixing to control them together.

Having each channel on stick axis would have you move both sticks forward to drive forward and both sticks backward to drive backward. Turning would be done by moving the sticks different amounts or different directions depending on how fast you want to turn. The benefit of this method is that it's easier to set up. The downside is that your Tx probably doesn't center the vertical axis on one of the sticks. This would make it hard to control. Some transmitters have the ability to turn on centering on that axis by opening the case and adjusting a screw or spring. I don't know if that's an option on yours.

Thr other way you can control your channels is by mixing the inputs (stick movements) to the outputs (commands sent to motors) using the menus in the Tx. This takes more work in programming the mixes in the Tx but would allow you to control movement with one stick by pushing it forward to drive forward, backward to drive backward, and sideways to turn. The mix would convert the stock position into the commands needed for each motor. I would probably try this method first and use the other method if it takes too long to figure out the mix.

For power on the robot, you have two considerations. The receiver and any servos you want to drive will need 5V. The motors will need whatever they are rated for. Batteries do not come in 5V so you will need a voltage regulator (called a BEC in hobby parts). If you want to drive servos, make sure you get at least 2A. 3A is better. If you're just offering the receiver then 1A is plenty. You can connect the voltage regulator in parallel with the motor drivers on the same battery to keep the part count down or use a separate battery for redundancy.

Powering the motors will require a circuit that can convert a pwm pulse into a DC voltage that can go either positive or negative relative to the motor's ground. You can make a circuit to do this (H bridge) or buy one (electronic speed controller/ESC). Buying is obviously easier but making it can be rewarding if you have the electronics knowledge and time. I made one once and will probably never do it again. If you choose to buy an ESC make sure it is for brushed motors and supports reverse.

DC motors are brushed. Brushless motors use switched 3 phase current and are harder to control. You wouldn't want to try making the circuit for that.

I'd suggest buying a couple of brushed speed controllers and hooking the motors up to the receiver early on just to start playing with how the controls work and how everything hooks up. Something like this would supply up to 10A at 8V and has a BEC built in to power the receiver without a separate voltage regulator. Your motors are rated for 12V so you would want a esc that's rated for 3S batteries to get full speed from them at 12V. You can drive them at lower voltage, they just don't go as fast. With a mac shipped off 50RPM you'll probably be fine driving them at lower voltage if you choose to. https://www.amazon.com/Hobbypower-Brushed-Motor-Speed-Controller/dp/B00JXI3H6Y/ref=pd_aw_sim_21_3/135-3030252-4248969?_encoding=UTF8&pd_rd_i=B00JXI3H6Y&pd_rd_r=88ce235c-2f84-11e9-b749-21300a56b15d&pd_rd_w=Uj4Q1&pd_rd_wg=9ylcL&pf_rd_p=469620d9-3e90-496d-9dc8-b19f900ba5fe&pf_rd_r=YJG0RZ5J9R6H8JS09SBX&psc=1&refRID=YJG0RZ5J9R6H8JS09SBX

Sorry for the long link. I'm on mobile.

Batteries are another thing altogether and would require a separate post. If someone else is making the offer system, get with them early to figure out the battery voltage so you can pick the right speed controller.