Now go to APE's File menu, and select open. Use the arrow keys to select firmware.h and open it. You now have two files open in APE. You can toggle between them using Ctrl+t.
Check the values of LEFT_DRIVE_PORT and RIGHT_DRIVE_PORT in firmware.h. Make sure your robot's drive motors are plugged into the same port numbers set in firmware.h. If so, you should now be able to drive your robot using the firmware you just compiled and installed!
From here on, programming will be a process of exploration and experimentation. Try modifying your robot and the code to add additional drive motors, implement motors and/or servos, and simple sensors such as button sensors or light sensors. Study the source code and the OpenVex API Documentation to see what functions are available and how they are called.
When you feel you've mastered the Beginner code, go to the Advanced directory, and begin exploring the code there. The advanced code contains examples of autonomous operation and many different sensors.