Savge Worlds Universal Information
Multiple wounds are only caused by raises (plural), correct.
So a Shaken character with a Toughness of 5 takes one wound if hit with damage from 5-12 points (a success through one raise). At 13 points (two raises), he would take two wounds and so on.
Note, the tricky part is that it doesn’t add to the effect of raises. So a success causes one wound and a single raise also still causes one wound (two raises = two wounds and so on).
Think of it as a Shaken character being easier to hurt (cause one wound) but not any easier to severely hurt (two or more wounds).
If a character is successful in Soaking all damage done by an attack, then they get an added benefit of removing any Shaken condition they had (or would have gotten from the damage as well) as well.