Double Click to select an entire object (single click will select a face, edge or vertex, which is explained in Modifying Faces Edges and Points.)
Click and move the circle to the point you will use as the snap point.
Click and then start dragging. You are now moving the object and the preselected point will now be your snap point.
Press the tab key. You can now type in a specific distance to move that object along the current axis.
Right click on the cube. You will see the Context Menu.