Hold down the middle button on the left of the watch face to enter the "Settings" menu. Using the lower left hand button, scroll down to "System" then press the top right button to enter the menu. Next, scroll to the "Connectivity" menu using the lower left hand button and press the upper right hand button to enter. Once done, you'll have two options – "Phone" and "Wi-Fi". Select "Wi-Fi" and enter that menu with the top right hand button.
Scroll down to the "My Networks" option and enter. Inside, scroll to the option marked "Search for Networks" and select it. Your watch will then perform a scan where it should find your network. Once done, you'll need to select it with the upper right hand button. You'll then go straight into entering your Wi-Fi password – which you can do using the selection buttons or touchscreen if your watch has one. Once your password is correctly entered (selecting the required letters and numbers is a pretty fiddly task), your watch will be connected to your Wi-Fi.