The older technology being a 2 stroke has a simple system which needs two types of oil to survive. One being Dirt Bike Gearbox Oil which is used to lubricate your bottom end bearings, clutch and transmission.

A decent motorcycle gear box oil designed for wet clutches will be around 80w which is a number to quantify the viscosity of the oil. Avoid using cheap oils or oil made for cars as the viscosity will not be the same and this may damage a motocross bikes high performance engine.

For the top end of your two-stroke motor being the piston, rings and top end bearings a different type of 2 stroke oil is added to the fuel at a certain ratio to act as lubrication which is burnt up upon combustion. Typical fuel/oil ratios in two-stroke racing machines are from 20:1 to 50:1 and everything in between. 

20 parts fuel to 1 part oil = 20L of fuel to 1L of oil

Always check your owner’s manual to see what the recommended ratio and brand of oil is for your particular bike as too much or too little oil in your fuel can lead to engine damage or seizure!