So, probably he most common type of vibrato is what I have labelled the "push/pull" vibrato. This is the vibrato that most of us learn from the get go. Grouping several fingers together (often) and pushing the strings by manner of extending your fingers (how much depends on the pitch of the vibrato, and the desired effect).
You call also "pull" todwards the floor by simply closing your hand. This sort of thing is easier shown than clad in words, so check out the vid guys!