You'll see a button saying "Drag ROM file or click here". To load your files:
Tap on the button mentioned above.
You'll have to know how to access and open your phone's files due to different models having different ways of access.
Open up your ROM.
Once you select the ROM from your files, the player will load up. There will be an advertisement too; simply wait for the X to appear in the upper-right corner to close the ad.
If the system is not auto-detected, a list of supported systems will show up. Select the system the game is for, then the player will load up correctly.
Once the player starts, the Virtual Gamepad will pop up. Depending on the system, the controls will change to fit the controller Tapping on the 3 bars in the upper right-hand corner will bring up the menu. On the left side, you have all the options - Restart the player, pause/play the player, save state, load state, start screen recording, and cheats. On the right, extra settings.
Restart Player - Restarts the player.
Pause/Play Player - Pauses/Plays the player.
Save State - Saves the exact moment you're seeing in the game as a .STATE file.
Load State - Choose the .STATE file you saved for the game (file will have the name of the ROM), and begin exactly where you left off.
Controls - Change your controls for the system. Most controllers are supported and controls can be binded to buttons on your controller, or to a wired keyboard.
Start screen recording - Records the game so that you can save a video of gameplay.
Cache Manager - Manages caches. yeah.
Cheats - By entering Game Genie cheats (you can find these online for the game you're playing) You can achieve crazy things.
Extra Settings - Change the shader, aspect ratio, Player Pak (N64), and many other things.