It will only go in one way -- you cannot really make a mistake and wind up with it jammed -- if wrong, it will simply refuse to get plugged in.

Anyway, look at the mount (underside of the lamps) and envision that it is like an arrow. There's a narrow end (where there's also a "spring-loaded" flexible piece of plastic), and a wider end -- the narrow end is at the "pointed" end of an arrow, and the wider end is at the spread "tail feathers" of the arrow. Just remember that the arrow points forward.

[And to remove, just slide the lamp forward [where it will compress against the aforementioned flexible piece of "springy" plastic to allow it to move] and the rear or trailing edge can then be popped out.

Hope this (made sense and) helped.