From the official Fightcade website -
THE BEST WAY TO PLAY RETRO GAMES ONLINE
Fightcade is a matchmaking application for playing retro games online, bundled with different emulators for seamless online play. Free, and without ads!
Go to the official Fightcade website and download the program by choosing your computer operating system (windows, mac or linux) and make sure to make a fightcade account so you can play.
Install the file that you downloaded and make sure to see the directory it will be installed. (example: C:\Users\Your user name\Documents\Fightcade)
Download this FC2 JSON pack zip
(What this file does is basically instead of you manually downloading each rom for the games you want to play, this file downloads the roms for you as soon as you want to use them.)
Go to the directory i mentioned before (C:\Users\Your user name\Documents\Fightcade) and you will see a folder called "emulator" where the files inside the zip mentioned need to moved to. Open the zip and copy the files in the emulator folder
Im also leaving a video tutorial on how to install and play with Fightcade just in case here