Dummies Guide: RetroArch
If someone linked you here, they probably thought you were being a dummy. So go ahead, take your time, and start from the top.
Open the .7z file with 7zip or WinRAR, or other archiver of your choice and extract the files to where you want to install RetroArch, or if on console/phone, install it using the standard method for that system.
RetroArch doesn't come with emulation cores, so you have to download them yourself. However, RetroArch does have a built in updater. So to download up to date cores, scroll down to Online Updater, and select Core Updater. RetroArch will download a list of available cores to download, and you can individually download them. To see what core does what, see this list.
If for what ever reason RetroArch can't download cores, or wont display a list of available cores for download, you can get them from the buildbot here.
Running a Game
After downloading a core you can run a game by selecting Load Content → Select File And Detect Core and selecting your game.
If you have only have 1 core that can run the selected game, then RetroArch will automatically load that core. If you have multiple cores that are capable of running the game you'll be given the choice between them.
BIOS and System files
Some emulation cores require special system files, or BIOSes. These can be downloaded here. Extract the system folder in that archive to where you installed RetroArch (the folder where the retroarch program is. retroarch.exe on Windows).
Core Options, Core Specific Settings
To edit options or settings specific to a core, you must start a game with that core. After loading a game, press F1 or the Home/Guide button on your 360/PS3 controller to get back to RetroArch's menu. From there you can change Core Options, set core specific input options, cheats, and change shader settings.
Shaders usually either come in single .cg files, or as a group of files controlled by a .cgp preset file. If you want to use a preset, like CRT-Royale or Super-XBR, simply select Load Shader Preset under Shader Options and select a .cgp file. If you want to select individual .cg files, increase the Shader Passes and select a .cg file through Shader #0 (or #1, #2, etc.).
After selecting your shader setup, hit Apply Shader Changes.
Saves and Saving Settings
By default RetroArch will save settings when it closes, and will do so unless you put RetroArch in a directory that needs elevated privileges without running as administrator/root. Save New Config will save a new, different, config that wont be loaded the next time RetroArch starts.
It's probably a good idea to enable SaveRAM Autosave Internal (under Save Settings) so game saves will be written to your harddrive while RetroArch is running.
This particular core requires some specific care. You should have the correct BIOS (if not follow the BIOS and System files section), you'll also need to make sure your game has a metadata file in the form of a .cue, .toc, .ccd, or .m3u file. The most common metadata people use is .cue, and if your PS1 game lacks a metafile, you can create one.
An easier way to get around metadata issues, is to get your games from a better source. Redump PS1 games come in .bin/.cue format and work on mednafen without issue.
There's 3 different menu drivers for RetroArch to choose from, RGUI, GLUI and the default XMB. To switch between them go Settings → Driver Settings and switch Menu Driver. You'll need to restart RetroArch for changes to take effect.
You can change your wallpaper, text color settings, text size (DPI Override), toggle mouse support, and whether to display boxart in the Menu Settings.
You can change RetroArch's menu font, but it'll only work for the GLUI menu driver. To change it, under Onscreen Display Settings hit OSD Message Font and select a .ttf font file.
Should be noted that Onscreen Display Settings are for the yellow popup messages that RetroArch displays, and GLUI happens to use fonts from it, all of the other settings here only change the popup message.
Not all cores support cheats, you can check the Libretro wiki for which cores do. By default RetroArch comes with a fairly large cheat database, so to make a new cheat file, you can find files in the cheats folder of RetroArch's install directory for reference.To enable cheats, load the game, toggle RetroArch's menu, load a cheat file in the Core Cheat Options and you'll get a list of cheats available which you can toggle. After setting your cheats, hit Apply Cheat Changes. Some cheats may require you to Restart Content to take effect.