What kind of plate boundaries are possible and what are they like?

Adjacent plates can move
   toward each other (convergent boundary)
   away from each other (divergent boundary)
or
   past each other (transform boundary)
 

Convergent boundary:

Modern examples:
    ocean crust subducted beneath ocean crust:  Japan, Phillipines, Aleutian islands
    ocean crust subducted beneath continental crust:  Andes, Cascades
 
Continental crust can also converge with continental crust.  In this case, there is no subduction and the geometry is different from that shown in the picture.  Modern examples include:  the Himalayas, the Alps.
 

Divergent boundary:

Modern examples:  The mid-Atlantic ridge, the East African Rift, the Red Sea and Gulf of Aden
 

Transform boundary:

Modern example:  The San Andreas Fault

Image of the sea floor to show the locations of volcanic islands, mountain ranges, and trenches associated with convergence and subduction, and the mid ocean ridges associated with divergence.  In particular, the aleutian trench and the mid-Atlantic ridge are seen.  This image is copyrighted by Marie Thorp, 1977.
 

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