Instructions
Find a website which provides the Nintendo Gameboy Emulator online. A number of websites use this same emulator, which allows you play over 30 of the most popular Gameboy games, including some in color.
Click on the "Load Rom" button to pick the game you want to play. Highlight the game and click the "OK" button. The game may take a minute or more to load depending on the speed of your Internet connection.
Configure the game controls to your liking. The online Gameboy emulator allows you to configure your play by setting which keyboard keys control up, down, left, right, the a button, the b button, start and select. To change the key, highlight the key with your mouse and type the key you want to change it to on the keyboard. Use any keyboard keys you wish and hit the OK button when you have them all set.
Look for the X1 Video Mode and X2 Video Mode buttons at the bottom of the Gamboy emulator. Click on the X1 Video Mode button to make the game fit into the exact proportion of a classic Gameboy, complete with a visualization of the Gameboy. Play the Gameboy games in X2 video mode to expand them and make them larger and easier to see.
Use the controls you have set and play Gameboy games online just as you would with the real thing.