Basically a Vogel crystal is cut to amplify, coalesce, and focus thoughts and energy that you wish to direct into your body/mind or that of another person. The design of the crystal allows for your thoughts and energy (and the pervasive Universal Life Force), to enter the crystal at the receptive end, be amplified and focused as it travels in a circular pattern through the crystal, and be transmitted like a laser beam from the focal end.
In this way they are used primarily for healing efforts, both for sending healing energy to the body and the spirit; meditation to focus the connections with spirit world beings; and in efforts to focus our Life Forces on accomplishing our goals and dreams with laser like focus.
There is little really written on the uses of particular Vogel designs, but here is a short summary of what is known. For crystals of other cuts, you will need to work with them to determine their specific applications. Marcel Vogel pointed out in his teachings that a large number of facets was not necessary and that a crystal with 13 sides was more than adequate for all uses. However, current cutters offer a wider choice.
1: 155g 5.24"
2: 119g 4.5"