When you say:
my keyboard is completely different to what it is on all other apps.
I assume this means that the key bindings assigned to various operations are different than you expect them to be?
If that is the case, then the only way to have the bindings be like what you expect them to be is to manually change them all, and that menu option that you’re talking about is the place where you do it.
When you choose Preferences > Key Bindings from the menu, the window that opens shows you all of the default key bindings on the left, and your list of custom key bindings (for the current platform) on the right.
In order to change a key binding you need to find the operation that you want to perform in the left hand pane and copy it to the right, and then modify the keys to the key that you want.
For example, if you wanted to modify things so that copy is Control+Shift+Alt+C instead of Control+C, the entry is:
{ "keys": ["ctrl+c"], "command": "copy" },
which you would copy to the right and modify so that it says:
{ "keys": ["ctrl+shift+alt+c"], "command": "copy" },
With all of that said, I use Sublime on Linux, Windows and OSX and I haven’t found that the key bindings that it uses by default are that much different from other applications that I use on those platforms, so perhaps I’m misunderstanding what you mean by the keyboard being completely different?
