Why does '<,'> come up in Vim

Question

Sometimes when I press : from normal mode, it starts with : ' < , ' >. Why does this happen and what is it good for?

Answer 1

You are not in normal mode, but visual mode. When in visual mode every command starts with the visual mode range, '<,'>, automatically. This is useful if you want to run an ex command on your visually selected lines, e.g. :s, :g, and :sort. For more information see :h v_:.