Have is a verb. As an auxiliary verb, it often follows modal auxiliaries such as would, should and must.
The rocket would have been sent up yesterday, but the weather was bad.
Of is a preposition. It is almost always preceded by a noun or a main verb and followed by a noun phrase.
The delay of the rocket firing was due to bad weather.
In designing the rocket, the engineers thought of everything
but the weather.
Never use of after a modal auxiliary; use have.
We must of made a mistake.
We must have made a mistake.