The current version of watchOS allows you to call (via iPhone, of course) any of your contacts, and that's it.
With the app Watch Keypad, you get on your Apple Watch a numeric keypad and you can then call or optionally send a message to whomever / where you want (using Force Touch on the screen). That simple.
The numbers you dial with it are in a history, accessible both by the watch and by the Watch Keypad app on the iPhone.
You know what the coolest? The app was created by Tom de Ruiter, a boy of just 14 who participated as a fellow in the last two WWDCs.