When you install Linux Mint 13, you will have to choose whether to automatically login or to enter the password to login. Regardless which option you picked, you can easily enable or disable autologin later on.
Just open the menu, and go to the Control Center, then click on the "users and groups" tab in the System categories:
On the user settings window, there is a line for customizing the autologin feature. Click on the Change button:
And you will be presented to the "change user password" window, just check or uncheck the "Dont ask for password on login" option to enable or disable the autologin feature in Linux Mint 13: