I have a 1988 535i BMW. When i turn the car going slow it makes like a errrn sound (sorry best way to descripe it) I'm not sue if its the fluid or not. I want to add some just in case but i cant see down into the power stirring thing....theres like a metal thing as soon as you open the cap and then little holes on the side so i'm not sure how much is in there....can anyone tell me how much the car is suppose to hold...and if the mechanical parts just need to be greased

This may not have anything to do with power steering. Is it when you turn either direction? Or just one side?

There are several suspension parts that can make a noise so it is important to have more information on the noise or when it occurs.

-L & J

LJmotors is right about the noise.
this may be a worn suspension item.
when filling the power steering system on the E-28 535
model it is important to keep in mind that it is also the brake booster system too.
when filling the system, be sure to relieve the pressure
in the system first by pumping the brake pedal until
the pedal effort increases dramatically(engine off)
what this does is it allows the pressure reservoir(AKA
the bomb)to return to ambient system pressure.
failure to follow this method can hydraulically lock the system.

I have a separte brake fluid and power steering fluid thing....It happens if i turn the wheel either way....mainly when i go to back out of a parking place and when pulling into one slowly. When i'm up to speed it really doesnt sound like its making any noises....so i dunno if its the fluid or what

Yes the brake fluid is separate
the power brakes and the power steering are powered by the power steering pump.
I am sorry if I was not clear about that.
this does seem like a suspension item making the noise
unfortunately I am not there with you to help
diagnose this.
Sway bar links can cause this as well.
to isolate them from other causes, remove them and drive the car and if the noise goes away you found the problem.