How to add game to any emulator?

Without 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 opens with the game ready to play.

With 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 gadget icon on the right top corner. Hit the "Apps", then scroll down to the "File Sharing" section. Click GBA4iOS/iNDS, then drag&drop the games you wanna play.

IMPORTANT NOTICE: some emulators cannot open *.zip files. You’ll need to unarchive them before using on your iDevice.