How do I add a game to this emulator I've downloaded?

No worries, let us help!
If you do not have a Mac/PC: Open Safari on your iOS device, go to the website with ROMs you like, then find the game you want to download. Press the “download” button and wait until it completes. Once it finishes, tap "Open in..." and choose the compatible emulator. Then the app should open with the game ready to play. Enjoy!

If you do have a Mac/PC:
Download the game you want from any ROM website to your computer. Open iTunes with the iOS device connected, then click on the device icon in the right top corner. Click "Apps", then scroll down to the "File Sharing" section. Click GBA4iOS/iNDS/whatever emulator you downloaded, then drag & drop the games you want to play on your device. Enjoy!

IMPORTANT: Some emulators have trouble opening *.zip files. You will need to unzip them before using it on your device.