It just catch a big animal like me and get destroyed..

Are they doing it just to move around?

Traveling from one place to another is usually the case. Spiders can pull web in a light breeze, and this strand gets caught in an adjacent tree, and go from one tree to another.

An orb weaver may use such thread as a scaffold to construct their fancy web.

Often they may try to web across such places as walkways where we humans may walk through their web, but they can soon rebuild their web, or make it in another place.

The single main thread is only the first step in constructing a full web, and it is often the only thread that remains after the rest of the web has been destroyed.

It just catch a big animal like me and get destroyed..

Are they doing it just to move around?