VexCode is easier to start than PROS, unless you are an experienced C++ coder.
The best starting point is to learn about V5 motor API that has built-in PID loops. Take a look at rotateTo(), spinFor(), rotateFor() functions.
Then you can learn how to use V5 drivetrain classes: VEXcode, motor groups and drivetrain example - VEXcode Pro V5 Text Tech Support - VEX Forum
Then you can take a look at examples of autonomous code that other people had posted, like this: Strange problem with autonomous
Then you can learn more hands on coding algorithms: Very Simple Very Accurate Chassis Control Code Release - VRC > Tower Takeover (19/20) - VEX Forum
When you get comfortable with all above, then it may be useful to learn about PROS, okapilib and really advanced stuff like odometry: 7842F 2018-19 Robot Showcase - Flywheel Control, Odometry, Engineering Journals & More - VEX Robot Showcase - VEX Forum