To move a single object, you do not need to select it first. When this tool is active, clicking an object selects it and dragging the mouse moves it.
The direction of the movement is determined both by your mouse and by the current reference coordinate system. To restrict object movement to the X, Y, or Z axis, or to a plane defined by any two axes, click the appropriate button on the Axis Constraints toolbar or use the Transform gizmo.
Moving an object