On your SETTINGS>Global Helper Permissions page - if you let helpers trade shifts or drop/pickup shifts "At Will", they can simply trade shifts and post a shift to the Tradeboard and if someone agrees to trade or pick it up then the schedule is automatically updated without the coordinator's involvement.
If you allow pickup of Unassigned shifts "At Will", helpers can pick up shifts up to their set maximum hours per week - any shift putting them over their maximum hours per week will be sent to the Coordinator for approval.
SETTINGS>Global Helper Permissions page).
Example: John wants to drop a shift. He clicks on his shift and chooses to place it on the Tradeboard as a "drop". Jane sees his shift on the Tradeboard and clicks on the shift and agrees to pick up his shift. If you allow drops "At Will", the schedule would then reflect Jane as the helper for that shift. If you allow drops only with "Coordinator Approval", then the shift is removed from the Tradeboard and a pending trade request notification is sent to the Coordinator and is seen in the "What's New" section of the Coordinator Home Page.
To track who picked up or dropped each shift, click the shift in any schedule view and then click the Shift History link in the shift change window.