There are a few ways you could do this. The way I would probably do it is this:
Note that the
<space> should be a literal space, not the text
<space>. This simply applies the set of keystrokes
I-<space> to every line in the buffer. Uppercase
I enters insert mode on the first non-whitespace character of the current line.
Of course, if you don't want it on every line, and instead on a few lines, you could visually select the lines and do
This is the most straightforward approach. The other thing you could do is a substitute command. For example:
:%s/^ */&- /
Just as with the last command, if you visually select the lines you would like to do this to, you can run
:s/^ */&- /
instead to only do this to certain lines.