How does humus makes soil more porous.What happens when soil becomes porous?

first, humus is a dark organic matter of dead plants or animals.It does'nt make the soil porous.It helps to make the soil fertile.The presence of sandy soil makes a soil porous as sandy soil have space between them.This provisdes more air for the roots of the plant to breathe.
note-If I am not right, that humus doen't make a soil porous, don't mind it.
hope it helps a little!