Welcome Alex

Your best bet is to look in the 'Build Diary' section of the forum. You are far from the first to ask for help so if you look for other posts similar to your own asking for help you will find links and advice to get you started (saves us repeating ourselves over and over)

Some of the good build diaries are Tormenta/Range, 360/720, my own Team Eventorizon one isn't bad either.

For designing your robot you can use Sketch-Up, or if you can get hold of a copy Autodesk Inventor or Solidworks.

For controlling the robots, many make the mistake that you need some kind of operating system or controller like an Arduino or Raspberry Pi (though some people use them to add extra functionality to their machines). Thankfully this isn't the case. You just need a Transmitter, like a Spetrum DX6, a receiver such as an Orange AR620, and then speed controllers such as the Hacked TZ85A and finally motors/gearboxes like Ranglebox Saturn 16's and RS 550 motors.

Building a robot these days is easier than you might think, you just need to know which parts to use and how to use them effectively.