What are GearSwap and Yush?
They're two add-ons that come with Windower 4. GearSwap handles all your equipment changes, to ensure that you've got the right gear on before, during, and after you use your spells, job abilities, and weapon skills. Yush effectively replaces the in-game macro system with external files that are easier to maintain.
How do I install them?
You must first enable these addons in your Windower GUI. With FFXI closed, find your Windower folder and run windower/windower.exe. Once the UI opens, select Add-ons, then find GearSwap in the list. If there's a green downward-pointing arrow next to it, click the arrow, then click the bar to the "On" position. Now find Yush in the list and download / enable that too. Yush isn't required for GearSwap, but the two addons work together nicely.
Now log into SuperNova like you usually would.
How do I use them?
Your GearSwaps are controlled by .lua files in the windower/addons/GearSwap/data folder. For example, if you play THF, you'd make a file called windower/addons/GearSwap/data/THF.lua and open it with a text editor.
Similarly, your Yush macros are controlled by .lua files in the windower/addons/Yush/data folder. You can either name the file Name_Job_Subjob.lua or Name_Job.lua. For example, when I play BLM (no matter my subjob), I put my Yush macros in windower/addons/Yush/data/Wren_BLM.lua. But for THF I have two files: windower/addons/Yush/data/Wren_THF_NIN.lua and windower/addons/Yush/data/Wren_THF_DNC.lua. So create the files you want -- with your name and jobs instead of mine -- and open them with a text editor.
What goes in these files?
Well, LUA code. You're going to be a programmer! Don't worry; if the idea intimidates you, you can simply grab my files below, save them to the respective data folders, and make your own minor tweaks to them. However, If you want to learn how to create files like these from the ground up, I recommend Rotha's GearSwap Lessons. It's how I learned.
My GearSwap files
My Yush files
I'll soon be adding more of my jobs to this section.