I suppose you want to make a 1-PC "Multiplayer" game,
running the splitscreen for two people playing on that machine:


look up in the manual:

view camera2_view = etc...

this is the key to create two screens.
The rest is standard programming.
Just access two seperate character entities over
two seperate keymappings.

If you have the skill to make a singleplayer game, you
can also make a splitscreen two-player game..

(this section is more for network multiuser gaming,
better you post this in the programming section)