Cold Warm Occluded Stationary-Types of Weather Fronts

Why do we have sunny weather one day and heavy rain the next? Large air masses cause some of our weather. There are four main fronts caused by these air masses.
A cold front which is the result of cold air
A warm front which is caused by warm air rising over cold air.
An occluded front which is a warm air mass stuck between two air masses.
A stationary front which is two air masses with almost the same density and pushes against each other.