RetroAchievements is a third party service that provides achievements unlocking for classic games, just like any other gaming platforms like Steam or XBox. All your unlocks will be saved to your Retro Achievements account.
First, you will need to head on over to RetroAchievements.org and create an account. When you’re at the site, click Create a new Account in the top left corner of the page. Proceed with filling in all the requested information. Once that is all done, be sure to write down your username and password. This is important, as you will need these credentials later on in this tutorial.
Load a well known classic game. When you unlock an achievement, you will see a yellow message at the bottom of the screen.