I like to think of the digital sidecar and the breakout modules as converter cables. They take the multi-pin serial connector on the cRIO, and convert it into something that you can easily plug your own devices into. There are three types:
- The analog breakout is used to connect analog sensors like gyros and Potentiometers to the cRIO, and connects directly to the analog module
- The digital sidecar is used for a number of things, including sending signals to your speed controllers from the cRIO, taking input from digital sensors, operating the robot signal light, and controlling spike relays. The digital sidecar connects using the 37 pin ribbon cable
- The solenoid breakout is used to control pneumatic solenoids, using a 2 wire output. It connects directly to the solenoid module, much like the analog breakout.
Remember though, each breakout and sidecar needs its own power supply from the power distribution board.
I/O is input and output. The I/O ports on the sidecar can be used for digital inputs, like switches, or for small digital outputs, like lights. Larger digital outputs are best done using a relay.
Do you mean the compressor? If so, yes, it's used to refill the pneumatic system. Electrically speaking, it is connected to a Spike relay, which in turn is driven by a signal from the digital sidecar.
The D-link will be used for wireless communication between the Operator Interface and your robot during operation, allowing you to drive it. The converter ensures that the D-link receives the correct voltage.
Solenoids are connected through the solenoid breakout, or using relays. They are used to control pneumatic cylinders.
A lot of useful information on these parts can be found
here.