Instructions
Navigate to a search engine and search for a "GBA Emulator." Websites, such as The Emulator Zone, provide information on different emulators based on user votes; this will help you decide which one to download.
Scroll down to the bottom of the screen and click on the download link for your emulator of choice. Save the file to your hard drive, right-click on the downloaded zip file and choose "Extract All" from the drop down menu to extract the program. Open the resulting folder and double-click on the executable file to install it. Follow the onscreen installation instructions keeping all the default settings.
Perform another search for a GBA ROM. You will be directed to a variety of ROM websites, such as "Dope Roms," "ROM Freaks" and "ROM Hustler." Use the search box or alphabetic ordering system in these websites to find your desired ROM. Download them using the relevant ROM download links and save them to your hard drive.
Open your GBA emulator and select "File" and "Open" from the top menu. Locate the desired ROM and press "OK" to load the ROM. The game will take a few seconds to load and then you will be able to play GBA games on your computer.