I have dedicated hundreds of hours of my time, producing dozens of in-depth, detailed videos to help new builders such as yourself. Take a look: Just ‘Cuz Robotics Guides and Tutorial Videos
If you want some quick info as to what this sport is all about, start with the video above!
The Witchdoctor Junior YouTube video series is, I believe, one of the best starting points for a new builder if you have no real robotics building experience. It is geared a bit towards kids for their summer program, but it's perfect for anyone who is just getting started. This is by the Witch Doctor Battlebots team!
Other resource guides referenced here:
This should be the go-to in the future when it is more filled out.
Robert Cowan’s Resource Guide has a lot of overlap with this information presented here. He has a lot more commentary on the information/sources/services provided that you may find valuable.
Building Your First Robot - Guides
Beginner: Arizona Robot Combat Guide
ADVANCED: Riobotz Combat Robot Tutorial
Beginner to Intermediate: Just ‘Cuz Robotics Guides and Tutorial Videos