Jumping Down
If you intentionally jump from a height, you take less damage than you would if you just fell. The DC to jump down from a height is 15. You do not have to get a running start to jump down, so the DC is not doubled if you do not get a running start.
If you succeed on the check, you take falling damage as if you had dropped 10 fewer feet than you actually did.
Action
None. A Jump check is included in your movement, so it is part of a move action. If you run out of movement mid-jump, your next action (either on this turn or, if necessary, on your next turn) must be a move action to complete the jump.
Special
Effects that increase your movement also increase your jumping distance, since your check is modified by your speed.