First, you will need to get to System Preferences. Click on the  Menu at the top left of the computer screen.
You will see System Preferences fourth item down.
Click on that item.

When the System Preferences window opens it will look like this.
We want to click on Accounts in the System Layer as I've highlighted here.
Click Accounts

This is what my Accounts window looks like. To access it, you need to click the Padlock at the lower left corner.
Click the lock.

This is the Authenication window that comes up when you click the lock.
Enter the password for the computer. This is the password you use to log into the computer or install software on it.
Click the OK button when you're done.

To add a new user, click the '+' symbol under the list at the left.

This is the new user account window. 
For this we're just going to make it a test user.
In Full Name, type 'test'
In Account Name, it should print 'test', but you can type that in anyway.
Don't put in any password.

This is how the window should look if you've done it properly.
Then click Create Account.

Apple doesn't want you to create an account without a password.
Click the OK button here.

This is how it should look if the account is properly created.
Click on Login Options at the bottom
This window should be visible. Make sure Automatic Login is OFF

Now, Log out of your account.
Go to the  Menu, Go to the bottom and Log Out.
You will automatically be closing all applications that are open. If it stops because something needs to be saved, save it and it should continue to shut down, or go back to the  Menu and Log Out again.
You will then see a Log In window
Choose Test and click Login. No need for Password.
It should take a few minutes as this is a new user. But once that's done, it should run fine.