How do I erase?

Before you can erase anything, select the eraser tool as in Figure 1. Then erase, using a pencil/stylus or a finger.

Figure 1: A selected eraser

You can erase with precision from strokes and images, as shown in Figure 2.

Figure 2: Erase from image

How do I erase only from the current selection?

Smart erase mode is a feature for erasing only from what's currently selected.

Smart Erase mode activates when the eraser is active, plus there is a selection. In this mode, selected items will be sharp and unselected blurry. As shown in Figure 4, only the selected items will be affected when you use the eraser.

Figure 4: Using Smart Erase to erase only from selection.

To exit Smart erase mode, you can deselect the current selection, choose another drawing tool or enable lasso mode.