Things You'll Need
Instructions
Download and Extract the Emulator
Go to http://www.emulator-zone.com/doc.php/genesis, scroll to the bottom of the page and select a Sega Genesis emulator to download. Fusion works well.
Open the .zip file using an extracting program, preferably WinRAR.
Select all files and click the "Extract To" button on the top toolbar. Make note of the file name you select to extract these files to.
Download a Rom
Download a "rom," or virtual game of your choice, from http://www.romnation.net/srv/roms/genesis.html, or do a web search for "free genesis roms" and you can find a number of sites hosting free rom downloads.
Open the .zip file using an extracting program, preferably WinRAR, the same way you did for the emulator.
Highlight all of the files and select "Extract To." Extract the files to the same file folder as you did the emulator.
Starting the Emulator
Open the file folder where you extracted both the emulator and the rom.
Drag the rom file over top of the emulator .exe file and the emulator should automatically start up and bring you to the menu screen of the Genesis game.
Use the keyboard as the Genesis joystick. The directional buttons and "Enter" key should function as the directional keypad and "Start" button. The A, B, and C configuration varies between emulators.