Either plain hot water (as in tea- or coffee-making); hot vegetable oil (as in saute frying); or organic solvents such as alcohol (as in an herbal tincture) will work to extract psychoactive compounds including those found in cannabis.

Since alcohol is flammable, it can be dangerous to goof with unless you use common sense and take some precautions. I think that alcohol will do the best/quickest job, but if you keep extracting over and over again, you'll get most if not all the active ingredients out by using any of those: water, oil or alcohol.

I've heard the process called "alkaloid extraction" (although THC isn't an alkaloid, since it doesn't contain any nitrogen), or "chemical (or herbal) maceration".

You'll end-up with everything that is soluble in that particular solvent: not just the "fun/good" stuff. With cannabis extracts, these other compounds won't hurt, but may be the bad-tasting stuff. I don't know if JUST the fun stuff would taste bad or not: perhaps it would taste like a good toke off of a vaporizer.

Anyway, with other psychoactive plant extracts, the extra stuff in the solution is OFTEN harmful, causing bad side-effects. In those cases, further processing can separate the fun stuff from the junk. Depending on what you want and what is junk, a different type of solvent (polar vs non-plolar, or protic vs non-protic solvent) is chosen to further extract-out the undesirable compounds.