The mind of the Buddha is traditionally represented by a stupa of enlightenment, but you need not go out and buy a costly silver or gold one. A photograph or a clay model is perfectly acceptable. The stupa [Tib.: chorten] should be placed to the right of the Buddha image, or below the Buddha if the altar consists of several levels.

(Text came from here)

A picture is worth a thousand words. Trying it out is better yet.