You can mark regions on images by holding down Ctrl and dragging down and right with the left mouse button. You can move the region about by dragging on the label with the left mouse button; you can resize it by dragging with the left mouse button in the border; you can get a useful context menu by right-clicking on the label; and you can pop up a box which will let you edit the region numerically by double-left-clicking on the label.
If you drag up and left, you will make an arrow. If you hold down Ctrl and just click the left mouse button, you will make a point. If you drag from a horizontal or vertical ruler, you'll make a guide. Guides are useful for lining up other things in the view window.
Use File / New to make regions, points, arrows and guides without the mouse.