I have been through that phase, but luckily there is a detailed guide for installation of Fabulously Optimized!

https://fabulously-optimized.gitbook.io/modpack/readme/install-instructions

So basically there is option for two launchers, one is Curse forge (by Overwold) and second is MultiMC.

MultiMC has auto updates and is much faster than curseforge, whereas curseforge has a much simpler interface but launch is a little slower compared to multimc since cs uses vanilla client, So choose wisely!

Dm me on discord if you still need help with anything 🙂