The short answer
Delta Emulator loads classic game ROM files stored on your device and plays them with on-screen controls, save states, and retro rendering. It does not ship with games, and it does not download them for you. Think of it as the console; you bring the cartridges. If you have not installed it yet, start at the Delta Emulator official site.
Which files work
The app targets classic handheld and console game files in the common ROM formats players actually have: Game Boy, Game Boy Color, Game Boy Advance, and NES-style files. Keep your library organized by system in separate folders; the library scanner picks them up cleanly and box art (where the app finds it) lines up correctly.
Organizing your library
Create one folder per system inside a top-level Games directory, with file names that include the game title and region. Short, consistent names make the library view readable on a phone screen. After adding files, use the in-app rescan rather than reinstalling anything.
The only rule that matters
Emulators are legal software. ROM files are copyrighted works in most regions. The line is simple: play games you own or that are freely distributed (homebrew and public-domain releases are a great way to test a new setup). This site does not provide ROM files, and neither does the app.
Getting the best picture
Once a game loads, open the video settings. Pixel-crisp integer scaling looks sharpest on modern phone screens, while the CRT-style filter adds scanlines for the full nostalgia hit. Integer scaling plus the filter is the combination most players settle on; the lag fixes cover what to do if a filter costs too many frames on older hardware.
