How does a fixed-focus lens focus? He has determined the focus. Is there a distance limit for photography? Focus on walking?

Fixed focus is the specified focal length, not fixed focus. The focal length is fixed, and you have to move your feet to shoot, which has certain restrictions.

Generally, a fixed-focus lens has only one manual focusing ring, because it can't change the focal length like a zoom lens. Its focal length is fixed, but its focus is never fixed (because the focus is different). You can focus from infinity to the shortest distance that the lens can shoot, so you can see that some lens windows have signs of infinity and the value of the shortest distance that the lens can shoot, which means that the lens can focus at this distance. The so-called autofocus of a fixed-focus lens means refocusing without moving the focal length, just like a zoom lens. In fact, zoom lenses can also be used as fixed-focus lenses, provided, of course, that you don't change the focal length.