A pyramid is a three-dimensional figure with a polygon for a base with 3 triangular sides (unlike a prism, which has 2 bases).   We name pyramids based on the type of polygon that makes up its base.

The figure below is an example of a triangular pyramid (its base is a triangle):

The figure below is an example of a rectangular pyramide (its base is a rectangle):

Note that the height of a pyramid is the perpendicular distance from the vertex where the triangles sides meet at the top of the pyramid to its base.

The formula for finding the volume of a pyramid is:

V = Bh/3, where B = the area of the base and h is the height of the pyramid.

Be careful finding volume in that you don't mix up the height used to calculate the area of the base (such as in the case of a triangular pyramid) and the height of the pyramid.

The formula for finding the surface area of a pyramid is:   

1/2(lp) + B, where l is the lateral height (sometimes called slant height), p is the perimeter of the base, and B is the area of the base.