On the LEFT side (drivers side) is the hydraulic fluid for the self-leveling suspension, is this what you mean? It's under a cover up front as you described, but for reference you should always call the drivers side the left side, the passenger side is the right side (assuming you have a left-hand drive vehicle)
If you look around the top of the reservoir, there should be a label quoting the part number of the fluid, it's dealer-only stuff.
If there is no label there, it should tell you in the owners manual. Also in the owners manual should be a diagram or drawing of the underhood area pointing out what the different service areas are for.