When you create a user, a group will be created with the same name and will be set as newly created user's primary group.
You can find out what your primary group name is using:
The file which defines which group is your primary group lives at:
/etc/passwd, run bellow command to get corresponding line to your user:
getent passwd $USER
it should look like:
Pay attention to second (1000), it's your primary user's group id.
or find out what groups your user is a member of using:
The file contains details about groups lives at:
/etc/group, this command should show you the details about your user's primary group:
grep "^$USER" /etc/group
getent group $USER
The result looks like:
Remember the 1000 from before? this is the group id which has been set as your primary group in
Then when you create new files, they would be owned by your user, and your primary group (which is same as your username and only one user is a member of that group, which is your user).