Its a two stroke engine and so it needs two kind of oil.
The first is two stroke oil, this is put in the plastic tank on the side of the bike and is pumped directly to a spigot on the side of the carburettor (you may see this pipe coming from the front right of the engine into carb). There is a red coloured oil level warning lamp for this, it should be on permanent in neutral (this is a lamp test facility) and if its on when in gear the level is low and should be topped up immediately. Note if this tank is empty you will have to bleed the pump when you top it up. Because of this set up the is no requirement to pre mix oil/petrol, BUT if you dont know the history of this bike you need to verify that the oil pump is still fitted and functioning (its under a cover at front of engine), and that the cable from the throttle is still functioning on the pulley of this pump. The cable and pulley allow the pump stroke to increase as the throttle is opened wider and vise versa.
The other oil is the gearbox oil, you will see a drain plug under the engine.
the filling point and dip stick is behind the kick start lever. Use SAE 10W/30 motor oil in here. when settin level from dip stick, hold bike vertical and dont screw dipstick in when dipping.
The air filter is an oiled foam type, you do not have to discard it if it looks ok, just wash it in a little petrol (work safely) squeeze out excess petrol but dont wring and leave it to dry, then applly a little two stroke oil and work it in thoroughly, it must be damp but not dripping.
Have fun!...Great bikes these