It may cause "convergent or divergent boundary"
It depends upon what kind of plate will collide. If continental to oceanic, the oceanic plate will subduct and melt to form a magma. On the other hand, the continental plate will form volcanoes, mountains etc. Trenches will also be formed. When water mixes with the magma, it makes the magma less denser thus producing volcanic activities. There's a difference when both continental plates collide and oceanic to oceanic.
Dive and Discover : Plate Tectonics : Collide. When two plates carrying continents collide, the continental crust buckles and rocks pile up, creating towering mountain ranges. The Himalayas were born when the Indian subcontinent smashed into Asia 45 million years ago.