I agree with all that has been said. With that said, when you add fluid, make sure you burp any air that may have entered the lines. As you move the wheel to the right and left as mentioned, have the person watching the fluid note if air is coming out, thereby lowing the fluid level. Add fluid and as needed to make sure the level is full and no more air (if you had any in the lines) is coming out.
I also agree that you should use the same fluid that is currently in the system. Mixing fluid can cause damage. If you know the brand / model of your system, the manuf may have PDF manuals on-line or someone in tech support might be able to give you addtional instruction for your system.
I wrote to a vender about a old inverter model that presented very strange behavior. As it turned out, the fix was not something I would have thought of and was as obscure as the systems. I followed his instructions and like magic, the system functioned correctly.
I has to add a lot of fluid to my system last summer after removing an old *and installing a new autopilot pump on the boat. This had to be tied into the steering system. In my case, as you would expect, there was a lot of air to purge. Also I wish I had the oil can, with a small funnel and hose, it was still a mess.
Good luck.