how to check oil in engine driven???

i bagged the front of my truck but i dont know how to check the oil in my compressor. the dipstick has notches on it there is no full/low anything so im lost. and also how far in is it supposed to go? cause i dont think mine is going down as far as it is supposed to. its at a funny angle (the dipstick not the compressor) in the engine compartment with lots of stuff in the way