moving or deleting files

How can I move file with syncthing from folder A to folder B. Or copy file from folder A to folder B and than delete it from folder A?

Copy or move the file on your computer. Syncthing will sync the change.

I can do that when file from folder A is copied to folder B, so how I will know when file from folder A is copied to folder B so I can delete it, automatically? I am asking because files are 40Gb an it takes alot of space.

It will take double the space while it’s copied, there is no way around it.

As for how to know, you can look at the remote device sync status in the GUI. If they’re at 100%, they have applied the copy.

I don’t care about that as long as I can automatise this so it will delete file on source when it is copied!

No, syncthing is a sync solution, not a backup solution, it won’t randomly delete files because they got copied somewhere else.