There are two differents types of cannabis Oil, both for medical use, CBD-Oil the legal one, and Cannabis Oil with high percentage of THC. The most practise use to make your oil yourself is the so called "Rick Simpson's methode" as you can see in the video below.
IMPORTANT SAFETY NOTE:
While the method described in this video is very safe, it's important to note that the safety stems from following the instructions to a tee. ALL solvents are highly flammable and MUST BE treated with extreme caution and care.