Well the most common ways of collision detection are Bouncing Box and Radial Collision.
Radial Collision works by imagining there is a sphere around the object, defined by the objects center position and its radius. Then you do some simple checks like:
distance = pos1 - pos2; // Different in Positions
If Distance < obj1.radius + obj2.radius //Checks if the distance is less than the two radius together, if so then they are probably colliding.
The above isn't proper code btw.
