Review the available VEX V5 parts at www.vexrobotics.com.
Watch these videos about simple drivetrains and mechanisms: drivetrains mechanisms bar lifts double reverse four bar lift
Search Youtube for "VEX RI3D" (robot in 3 days) and "VEX Reveal" for robots designed for the current game.
Request an Onshape account from Mr. Moehnke (if you don't have one)
Add the VEX V5 Parts Library to Onshape: pdf
Watch Creating a VEX Robot in Onshape Explained By Mr. Moehnke: Video Part 1, Video Part 2
Watch Assembling a Robot in Onshape Explained by an Onshape Rep: Video
Watch Using VEX Chains in Onshape Explained by an Onshape Rep: Video