Drag the symbol to a position near the target element. The symbol automatically aligns itself with the element.
The symbol is now associated with the element. If you move the element, the symbol moves along the element.
If you move the symbol, it moves along the element, but not away from it.
At this point, if you want to associate the symbol and target element again, you can click the lock handle again. The symbol stays in the new position, but is now associated to the target element again. If you select another element or command after unlocking the symbol and moving it, you cannot re-establish the association with the target element.
If you want to unlock the symbol from the element, you can select the symbol and click the lock handle to unlock it. You can then move the symbol away from the target element.