For this tutorial you will need Steam, Boop (from SteamGridDB), and a little bit of patience.
The first thing to do when setting up your console-like interface, is to download Steam and add all your games.
To add Non-Steam games to your Steam library, you must click on the "Add a Game" button at the bottom of your Steam window.
Next, you must find the game files for whatever game you're trying to add to Steam. Epic Games, GOG, Ubisoft Connect, and EA games should work fine, but if they don't run without being launched from a specific app, they cannot be added to your steam library. Once you have located the game files, you must find the .exe file that launches the game, when you are certain that you have found the .exe file, double click it.
If done correctly, the .exe file should appear in the list of games to add. Click "Add Selected Programs" to add the game to your library. While you could leave the game like this, it is more convenient to add a proper name, and artwork to the game so you can easily tell it apart from other games. For this we will use SteamGridDB's Boop tool. To download the Boop tool go to www.steamgriddb.com/boop and download the tool for your corresponding system. Once you have downloaded the tool, extract the .zip folder anywhere on your computer and run "SGDBoop.exe" as an administrator.
With this, the Boop tool is set up, and we can add custom artwork. First, rename your game to something you can recognize. When you have renamed your game, go to www.steamgriddb.com and search for your game. Once you have found your game, either look for artwork that you like, or click "View Original Steam Assets." Once you have found artwork that suits your needs, click "Apply with BOOP (non-Steam)." In order for things to show up correctly, you must find a vertical and horizontal Grid picture. Next, look for your game, and click OK. Do this as many times as needed.
Once you have added a game, repeat that process as many times as necessary for your entire library. Once you have added all your games, make the Big Picture Steam UI the default at launch, as well as setting Steam to launch when your PC boots. With that, you should see your game in the Big Picture UI, with complete artwork.
The only thing left to do is to add your controller to your PC via Bluetooth or USB. Steam automatically translates PlayStation controller's inputs to Xbox for games that do not support PlayStation controllers, and there are many community presets for games that do not support controller at all. Simply go to the controller icon for the game and set it up as you wish.