When you first boot up and configure a Raspberry Pi, it sets up a Linux user account for you. You might want to add additional users for other people that will log into your Pi or for various other reasons. Here's the command to do that.
sudo adduser bob
This command starts the utility to add a new user with a name of "bob", which you would substitute with what you want the username to be. Your Pi will tell you a bit about what it does while creating the user:
Adding user `bob' ...
Adding new group `bob' (1003) ...
Adding new user `bob' (1002) with group `bob' ...
Creating home directory `/home/bob' ...
Copying files from `/etc/skel' ...
Then it will ask you for the password for the new user:
Enter new UNIX password:
Retype new UNIX password:
Simply type the password that you want the new user to have. Next, you'll be asked for note information about the new user for the Raspberry Pi:
passwd: password updated successfully
Changing the user information for bob
Enter the new value, or press ENTER for the default
Full Name []: Bob Redfield
Room Number []: 23
Work Phone []: 501-234-8967
Home Phone []: 501-678-9876
Other []:
Is the information correct? [Y/n]
You can leave all of these blank or fill them in depending on your needs. Once this is complete, you can log in with the new user by typing
sudo su bob
Where you replace "bob" with that of the new user. You can also log out of your user and log back in as the new one.
This will create a home directory for the new user, as well, at /home/bob -- with the actual bob of course.
This is how you create a new user on a Raspberry Pi, but it will also work on other GNU/Linux machines that run Debian, Ubuntu and many other distributions.
Here's how to delete a user, as well: Deleting a User from a Raspberry Pi.