Please note that there is a difference between V-tail mixing and elevon mixing, although they do a similar thing.

V-tail mixes the rudder and elevator, while elevons mix the elevator with ailerons. A v-tail plane will still have ailerons.

If you have a computer radio, either one is usually a pre-programmed function. If not, you need to mix them either mechanically or electronically. They make gizmo's that you plug the two servos into to mix them if you do not have a computer radio. They can also me mixed mechanically, which is really cool, but it's harder to do.