Use adduser instead of useradd if you are not totally certain useradd is the tool you want to use because:
1. useradd is a low level tool.
2. useradd will not add home directory for new user.
3. useradd will not add many other defaults for new user.
4. adduser is more user friendly (but uses useradd in backend).
5. adduser will create home directory.
6. manpages of useradd recommends use of adduser.
Use it like this:
sudo adduser <username>
and to add a system user which has no shell (cannot log in, but just run programs):
sudo adduser --system <username>
instead of
sudo useradd <username> -s /bin/false
Using adduser, the system user a home directory will be created.
See http://askubuntu.com/questions/374870/home-directory-not-being-created and http://askubuntu.com/questions/345974/what-is-the-difference-between-adduser-and-useradd for good reasons with links to manpages.