Custom advancement datapack in 1.21

I need help with advancement packs in 1.21. I made them before in previous versions and they worked, however 1.21 had a lot of commands changed as you know and I can't get it to work. I went to the new 1.21 generator https://misode.github.io/advancement/ but I don't understand it as I did with the older one. Can someone help me please? I don't understand the wiki either. It's just so confusing compared to the old advancement generator