Afraid starts with your open hands (or closed fists) by your sides, with the dominant hand around chest level and the non-dominant hand around stomach level. Then you bring your hands inward, in front of your body, palms facing inward and fingers spread in an open five hand.
The same sign is used in Baby Sign Language (and ASL) for afraid, scared, scary, and frightened. And remember, you want to look scared and frightened, so your facial expressions should match the hand signs.
Introduce afraid when you notice your baby in a situation that is causing them to be fearful. Because these tend to be highly memorable situations for your baby, they tend to make the connection to the sign quickly. Afraid is a useful sign for intermediate babies. It lets them communicate to you what events cause them concern. The things causing your baby distress can often be things we find innocuous, such as a loud blender. And once you know that something is causing your baby concern, it is usually easy to either avoid it or to help your baby overcome their fear. Often just naming the emotion does a lot to reduce their anxiety. Afraid is usually used when something unexpected and unpleasant happened. When the news is pleasant or neutral, we usually use surprise.
Teach your baby how to sign afraid when something causes them concern or anxiety. Signing afraid can help your baby avoid the cause of fear or overcome the fear, simply by communicating their feelings to Mom or Dad.