The Multi-Engle Piston (Landplanes) Class Rating Course, to give it its full title, is a short and straightforward course. If not combined with the CPL as explained above, then the course must include no less than 6 hours training, plus the test which last about one hour. There is a ground training requirement and an examination usually administered by the school.
The course is variously abbreviated as MEP, ME, MEP(L), or Multi; all refer to the same thing.
Although it is a short and straightforward course, it is important not only to pass the test, but also to be fully at home in the multi-engine aircraft before progressing onto the Instrument Rating (“IR”) course; there is enough new information to come to grips with on the IR course without having to worry about how to fly the aircraft. To that end, it is probably unwise to complete your ME course on one aircraft type then change to another for the IR course.