To put the cabinets in place you need to drill holes -- two for the supply lines and one for the drain. Use a hole saw because the diameter is slightly larger than the supply line (Image 1).
Take measurements and make sure once the cabinet is flush against the wall the door won't be hitting a windowsill or frame. If you need to put the cabinet an inch from the wall, you can use fill stock to cover it. Remove the cabinet doors for easier access.
They measured in 1" from the wall, made a mark and then measured to the center of the pipe. Then, they measured up from the floor to the center -- transferring the marks to the back of the cabinets.
Start cutting from the outside of the cabinet and then finish cutting from the inside; that way if it splinters, the rough cut will be against the wall and no one will see it (Image 2).