Check out the free Stihl MS 170 parts list for a diagram of your chainsaw, which can be found on this website from the manuals section, the service manual will provide good instructions also.
A few things to check to get you going, you will have to remove the black handle to access the hose that supplies the pressure to your oil tank. Once you remove the handle you will see the hose on the very bottom of the saw coming out of the crankcase and running to the oil tank. You will want to check the condition of this hose and make sure it is tight on the nipple on the block and that there is no cracks or tears, and that you can blow through into the oil tank without blockage.
You will want to check the tank itself for cracks also, and make sure your cap is sealed well and not leaking. Under your bar you will find the oil orifice that delivers oil to your bar, it will be a small metal puck pressed into the plastic tank with a very small hole in the center. Make sure that when you manually put pressure to the tank that this hole allows liquid to come out.
There will also be a auto oiler adjustment screw on the bottom that you can make small adjustments for increasing or decreasing oil flow.