Can anybody explain how impact craters formed on the underside of the moon, and how loose matter stays on the underside of the moon? 
I assume you mean for RET? and not FET?
From what I can discern from FET, you cannot definitively state that what you are seeing upon the face of the moon are in fact craters. The moon is only 32 miles across and travels in a circular path across the face of the flat earth. No-one has been to the moon, as that is seen as a hoax. So to assume that these deformations are in fact craters in FET is presumptious and is inherently a gross erroneous assumption.
For RET, the earth is in a lunar-synchronous orbit, so we always see the same side of the moon which is always directly facing the earth. It is possible (as stated above) that this may not be a perfect lunar-synchronous orbit, and over the span of thousands or millions of years, there may actually be a discernable rotation noticed. But even assuming that the orbit is perfectly lunar-synchronous, you would still have to keep in mind that the earth and the moon in RET are spherical, and a meteroite can still impact with the moon on the underside if it approaches at an angle across from the earth side.