Calab wrote:

- What is the optimum air pressure to supply the nailer with?

Probably 80-100 pounds. Air pressure may be the only way of adjusting the
depth of the nail. At the least, the air pressure will be a rough guide.
There may be a fine adjustment on the gun.

- Should that top actually adjust anything?

Nah, it's for the exhaust.

- Any links on how to use a brad nailer properly?

Aside from other tips, practice with scraps of the stuff you're going to
nail and the actual surface into which you intend to nail it. For example,
nailing a bit of moulding into wood will differ from nailing that same bit
of moulding into 1/2" of sheetrock before the nail hits wood.