You are right... it is not too complicated; sounds like the sprinkler guy is trying to ensure you call him in the future for help....

Anyhow, each manufaturer is a little different.... so the question is... what type do you have? I use toro and hunter rotors... they have a really good description of how to adjust them at www.toro.com
On mine, the left most part of the arc is permantly set, to adjust it you actually screw the entire head in further or less, depending on the need.... it is the right part of the arc that is trickier... the web site shows better than I can explain in writing.

On my heads, there is a tool that is just used to change out the nozzles (bigger holes provide more gph, ect), and a regular phillips head scre driver is used to adjust the exiting height of the water flow... had one head that was shooting almost striaght up once... a couple turns, and wala... it was shooting about 45 degrees.

Try the link

Here is a link that might be useful: Hunter sprinkler head adjustment

when initially installing a sprinkler spray head where should the top of the spray head be set? level with the ground? below ground? above ground?

Joe, if the heads are going to be in the grass area they should be flush with your final grade, if in a bed with bark, 1" above grade works to allow for the bark.