To switch on projection painting, activate the view you want to paint in (click in the view or click the view’s title bar) and enable the 3D painting mode icon on the left toolbar.
You will see a colored outline appear in the view to indicate that projection painting mode is switched on for this view. You can now paint.
Initially the paint is applied onto a projection layer, not onto the textures. To apply the projection layer onto the textures, do one of the following:
You may notice a delay while the projection is applied. Do not be concerned. Keep in mind that many calculations are necessary, especially if you are using large textures.