The more traditional string trimmer heads are the manual-feed ones. With these, you have to load the line and pull out a length before you do any cutting, ...

This brand sports five styles of cutting heads that utilize string on their trimmers: Speed-Feed (400 and 500), Rapid Loader, ...

To replace the broken line, you'll need to feed out more of it by either banging the grass trimmer on the ground (bump feed), stop using the trimmer and pull out more line (manual feed) or just start ...

Feeding out more line can be trickier on some trimmers, which will slow you down. There’s three types of line feed: Bump feed - where the grass trimmer is banged on the ground and feeds out new line.