If you really failed to read the big tutorial screen that appeared when you got a crippled body part, it seems that I must tell you it.
Just open your Pip-Boy, select one of the body parts in the Condition screen (That screen you first saw in your Pip-Boy.) and use a stimpak on it (S on PC or clicking it with the mouse, just look at the upper-right corner of the Pip-Boy screen).
Or then sleep in a bed. It gives you full health and heals all body parts.