What are the basic functions for foundations of buildings ?

foundations bare the weight of the building with its occupants and transmit evenly to the ground below .

to provide a level surface over which the structure can be built on . 

to protect the building from soil due to the soil contraction and expansion .

to provide safety to the structure from undermining elements like water or animals that might burrowing the ground below it .

it anchors the structure to deep in the ground and prevents it from sliding or falling due to horizontal forces like wind or ,seismic forces like earth quakes.