To choose a tool whose icon is currently visible, click once on its icon. Click the tiny arrowhead next to a tool icon to choose a related tool from a pop-out palette.
Or even better, choose a tool using its shortcut (memorize the boldface letters on the next three pages). If you forget a tool’s shortcut, just leave the cursor over the tool icon for a moment, and the tool tip will remind you . To cycle through hidden, related tools on the same pop-out menu, press Shift and the same shortcut key or Alt-click/Option-click the currently visible tool.