The Magic Wand and Lasso tool are most common when making selections. If, however, you want to make a more detailed selection you can use the selection layer.
First, open the ①Layer window. The uppermost layer, with the pink background, is the ②Selection Layer. Tap this layer to make it the Current Layer and then close the Layer window.
You can now use the brush or eraser to make a selection. The area that you have brushed over will turn a transparent blue. Please note that when the Current Layer is the Selection Layer it is not possible to choose colors (as there are no colors in the selection layer). If you want to apply colors you need to change the Current Layer back to a Normal Layer.
Open the Layer window and tap ①Normal Layer to toggle to the Current Layer to a normal layer.
When you close the Layer window you will be able to see the dashed lines the show where the selection is.
You could shade this with an airbrush or similar. In general, as outlined in ‘Use Color Fill for the Undercoat’ and ‘Making a Selection with the Magic Wand’, it is recommended that you create an Undercoat layer and then use the Magic Wand to make selections. Doing so allows you to easily select the area you want, no matter how many times you clear the selection.