We've put together some schematics detailing how to connect together all the components of a WatchDuino 2.
After that, if you load the WatchDuino software into the Arduino mini, you should have a functional prototype that you can interact with.
We made this schematic with Fritzing, and we've included the fzz file in the Watchduino repo. You can open it with Fritzing to have a more detailed view of the schematic, and highlight the connections, for easier building. The Fritzing software is open source, and there are packages for all mayor operating systems available to download for free at their website.