Just use the 'Add new group' button, enter the name of the group and the country.
Entering the group's home country is important to correctly identify the matches' time and date, used in the calculations. You can use geolocation, if you wish.
You can also set up your group's playing rate, in order to best initialize the algorithm, and a description.
You can add players and/or ghosts to the group during group creation, if you wish. You will also be able to add them later on, by editing the group or (regular players only) when you enter matches.