Looks like what you’re trying to do is set up a key binding to toggle the display of line numbers.
If that is indeed the case, you have put the key binding in the wrong file; you should select Preferences > Key Bindings
and add the binding to that file, then remove it from the preferences where your screen shot above shows it.
When you add it to the bindings file, make sure that you put it in between the [
and ]
that surround all of the content in the file, and if you have more than one binding in there all of the entries need to be separated from each other with commas.
The error message above is telling you that starting at line 8, column 1 there are unexpected characters in your Preferences.sublime-settings
file. Having a curly brace in that position violates the syntax of the configuration file.
Sublime uses JSON for many of it’s configuration files which includes the sublime-settings
and sublime-keymap
formats.