useradd command is a simple linux command that create a user account in one shot using various options.we have to manually add command line options like groups,home directory path, password,username.

For example: sudo useradd -g testuser_group -d /home/testuser -s /bin/bash -p my_password -m testuser

adduser command perform the same action but this program is more user friendly version. adduser command ask you series of questions while creating user  like first name/last name of user, creating home directory path,enter password etc.