A long click is used for moving elements while holding a tool in the hand or for adding an inscription to an element while holding a tool in the hand.
A long click is performed by pressing down the mouse button and holding it down for a short while (approx. 0.5 second). The cursor changes to show that move is active. When you release the mouse button, the cursor changes back to the tool cursor, and you can apply the tool in the hand as usual.