Cannabis, AKA marijuana, is a phychoactive drug that can be used for medical or recreational reasons.  
It's quite an interesting drug, can you tell me more about it?
Sure!  Cannabis can be used by smoking, vaporizing, or in food.
Interesting, are there any chemicals in it specifically that make it psychoactive?
Yes, the main phychoactive part of cannabis is called TCH, which stands for tetrahydrocannabinol.  Quite a mouthful lol.
Are there any other interesting chemicals found in marijuana?
There are 483 known compounds in the cannabis plant, including 65 cannabinoids
Wow that is quite a lot, it makes have some complicated chemistry.