I call this file my "Cheat Sheets Formula Repository". It's where I dump all of my favorite Google Sheets formulas. I literally use this tool every day.
Every time I create or come across a Sheets formula that I like and is complex enough that I don't feel like memorizing it, I add it to this doc:
As you'll see, for each formula, I include a description, an in-context example and a link to the blog post where I discuss it, if there is one.
My suggestion: add this to your browser's Favorites. I'll continue to update it regularly, so hold to it.
Hope it's helpful!