Think addons4kodi is the better place but i'm happy to help
You'll want to use the built in browser on downloader to search for Kodi. Go to https://kodi.tv/ click on download and select android ARMV7A
Once downloaded youll want to open Kodi and enable allow unknown sources in settings (this will let you use Piracy addons)
Take a pick of your addons, most people recommend using Fen and paying for real debrid (non debrid Kodi Is pretty terrible) it's cheap and allows you access to 4k content and far more availability of sources to choose from
I'd recommend Googling "how to install Fen" and it'll walk you through the steps (though ignore when it tries to recommend VPN's you don't need them when using a Debrid service)
Edit: Other than that the thing would be to use a Skin, however since you've mentioned that it's an older Firestick I'd just avoid using one since it'll be extremely slow and probably crash a lot
There's also Trakt that you can link with most addons, it'll allow you to keep track of Episode/movie progress