Is Double click better than single click?
Within a web browser, double-clicking is almost always a BAD IDEA. Double clicking a "submit" button on a bill-pay or purchase form will very often generate two payments for the thing in question. Then, there are some Flash-based games that end up using double-clicks internally for things.
What is the use of single click?
A single click or "click" is the act of pressing a computer mouse button once without moving the mouse. Single clicking is usually a primary action of the mouse. Single clicking, by default in many operating systems, selects (or highlights) an object while double-clicking executes or opens the object.