IN PRIMS we can chooses any vertex and find the minimum edge ...in such way we add vertex without forming cycle...at every time we include such edge which has minimum cost among all vertex we choose...and process continue..
SO NO COMPULSION ON CHOOSING VERTEX OR EDGE...
IN KRUSKALS..we must have to chooses such edge which has minimum weight and we have add edges as per increasing order of weight ...
SO IN PRIMS = CHOOSE ANY VERTEX AND FIND ITS MINIMUM EDGE and include that EGDE , VERTEX and continue process...