clashes happen kind of rarely. it happens when your oponent does a move at the same time you do and they just happen to use a move that is just as fast as the move you threw out.
so say you throw out an i16 move and your oponent does an i16 move at the same time and it connects, it will clash but its never planned out.
The basics are your strongest tool in SCV. Find a guy who is better at them and they can probably beat you with almost any character they have at least a general understanding of. That translates to learn them basics and be godlike at the game.