What you do in software is going to depend on what you do electrically. You have several choices to make. You can either wire your solenoids to the solenoid breakout on a solenoid module in your cRIO, or you can use Spike Relays. A cRIO solenoid module can power either 12V or 24V solenoids, but not both at once. You need to pick one or the other and make every solenoid you connect to it is expecting that voltage

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I'm going to talk you through the simplest method to code, which uses the solenoid module.
Assume you have a piston that extends (forward) and retracts (reverse). You will need to connect a solenoid to each direction to control the airflow. For our purposes, you'll generally want the solenoid on the forward end to be set to the opposite of the reverse end. That is, if you're applying pressure on the forward end, you'll want the reverse end to be open to exhaust and vice versa. You may mechanically use a double solenoid or two single solenoids, but either option will use two solenoid ports on your solenoid breakout and they can both be coded the same way.
In Labview, start by defining the solenoid ports in Begin.VI. You'll use a Solenoid Open, and a Solenoid Set Reference. The easiest method is to call it a double solenoid (even if it really is two singles), and assign the correct Solenoid Port to each end. Give it a better name than in my example (attached) - you want something that describes what it does and that you can spell consistently.
Then when you want to use it, use the Solenoid Set VI (other example).
Note that it's been two years since we used pneumatics, so I may have the following settings exactly backwards - test with care 
. Forward sets the Extend end to pressure and the Retract end to exhaust, Reverse does exactly the opposite. (Off and On, while present, are generally not settings you want. Off sets both to exhaust. On sets both to pressure.)