If you mean letters as in text, that's done with the DrawText command, here:
http://www.leadwerks.com/werkspace/page/documentation/_/command-reference/context/contextdrawtext-r731
For online multiplayer people use RakNet, as Guppy mentioned, or you can also use Steam:
http://www.leadwerks.com/werkspace/topic/9663-introduction-to-steam-code-in-leadwerks/
Finally, yes, you can do local multiplayer with two (or more) people on a keyboard. I believe you can also get controllers to work but Leadwerks doesn't have that built in, except for Steam controllers:
http://www.leadwerks.com/werkspace/page/documentation/_/command-reference/steamworks/