There are really only two basic ways. One way is to find a spot about halfway between the anus and where the scrotum leaves the body and press. The other way is to go inside the rectum and press towards the front of the body. For inside stimulation it's much easier if you are sexually excited, since that causes the prostate to become firm and easier to find.
If you want to use a toy there are two ways to find one that will probably work. The first is to find a "G-spot" dildo, vibe or probe - these have a curve that enables pressure to be put on the G-spot, which is the prostate gland in women. The other option is a prostate stimulator, but these are sometimes harder to "drive".
In terms of sensation, pressure, tapping, thrusting play that bumps against the prostate, side to side "waving" and vibrators are the basic stimulation variations.