After installing Ubuntu System, there is only a user you configured during installation except System Accounts and he is an administrative user.
If you’d like to add more common user accounts on System, Configure like follows.

[1] For example, Add a [soncq] user.

sudo adduser soncq
[sudo] password for ubuntu:  # input self password
Adding user `soncq' ...
Adding new group `soncq' (1001) ...
Adding new user `soncq' (1001) with group `soncq' ...
Creating home directory `/home/soncq' ...
Copying files from `/etc/skel' ...
New password:           # set user password
Retype new password:    # confirm
passwd: password updated successfully
Changing the user information for soncq
Enter the new value, or press ENTER for the default
        Full Name []:   # input user info (OK with empty all if you do not need)
        Room Number []:
        Work Phone []:
        Home Phone []:
        Other []:
Is the information correct? [Y/n] y

[2] If you’d like to give privileges to a new user, Configure like follows.

sudo usermod -aG sudo soncq
su - soncq
Password:
# try to run a command which requires root privilege
sudo ls -l /root
[sudo] password for soncq:     # input self password
total 4
drwx------ 3 root root 4096 Apr 22 13:31 snap

[3] If you’d like to remove user accounts, Configure like follows.

# remove a user [soncq] (only removed user account)
sudo deluser soncq
# remove a user [soncq] (removed user account and his home directory)
sudo deluser jammy --remove-home