The Liberty Vaginal probe should be inserted with the rim facing upwards and downwards, with the metal electrode plates to left and right (outwards towards your thighs).
If you orientate the probe incorrectly, you may only have sensation on one side (however this can also happen if you suffered nerve damage during birth).
Insert until the rim at the base of the electrode is sited between the labia. It's fairly difficult to get this wrong. If you don't insert it far enough, you will probably feel that the stimulation is in the wrong place.
If you do not feel any sensation at all, you may require a larger probe.