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.
When Projection Painting is enabled or camera or material changes are made, BodyPaint 3D will require a moment before Projection Painting is ready to use again. A corresponding message will be displayed in the status bar.