Your bike should have an oil tank under the seat if it hasn't been taken off.
You fill the tank and it'll supply oil to the petrol through a pump automatically.
That is unless someone has taken the tank off and thrown it away, or disconnected the tank etc, in this case you'll need to premix your petrol/oil
2 stoke's use the oil added to your petrol to lube the crank etc.
They usually run 10W30 or 10W40 gear oil in their gearbox's, use a motorcycle specific oil if you can as they have a lot of additive's to cop with the high heat etc
Just make sure it's not a synthetic, or if it is make sure it is safe to use with wet clutch's.
Premix petrol/oil i would run it at 32/1, so 30 litre's fuel to 1 litre of oil (3.2 litre's fuel/100 ml's oil)
Oil brand's are up to you, i normally run Castrol Active 2T through my bike's