Remove a green screen
Chroma keying replaces one layer with another behind it, which needs layers on a timeline. The full editor does it with tolerance controls — this page takes you there.
Keying is not just deleting a colour, it is deciding what appears where that colour was. That means at least two layers.
The editor has tolerance and edge controls, because the difference between a clean key and a fringed one lives in those two settings.
Preview is live, which matters here more than anywhere: keying is judged by eye, frame by frame.
FAQ
Does it have to be green?
No, any reasonably uniform colour can be keyed.
Why are the edges fringed?
Usually uneven lighting on the backdrop. The edge controls help; even lighting helps more.
Can I key part of a clip only?
Split first, then key the piece.
What goes behind?
Any other clip, image or colour on a lower layer.
Is it free?
Yes.