Step 1: Tools
Step 2: Timer
You will need a timer. These cost about $30.
Step 3: Shut off valve
Step 4: PVC Pipe And Fittings
PVC fittings. Depending on your setup, you will need Tee's, 90's, a few of each. These are cheap, only $.25 - $.45 ea.
PVC adapters. Depending on the type of timer and your water supply, whatever you need to connect the timer to the supply.
Glue! Don't forget the PVC glue.