If you use the manual method 4 short presses then note the following:
Note: newer firmware uses 6 short presses.
With this option the switch starts as a Wireless Access point. The SSID on mine was sonoffbasic-1122.
You then need to connect a computer to this access point and go to the IP address 192.168.4.1.
You can then enter the SSID and password of the Wi-Fi network you will be connecting the device to.
When you enter this information into the webpage the switch will restart, connect to the Wi-Fi network and acquire an IP address.
Now in order to configure it further you will need to know the IP address it has acquired.