I will use Vue js as I like it a lot. Won't run my own auth and I already implemented client side auth with auth0 and Vue. But I wouldn't know how to let people

I will use Vue js as I like it a lot. Won't run my own auth and I already implemented client side auth with auth0 and Vue. But I wouldn't know how to let people auth server side for example. Auth is a really deep rabbit hole and unfortunately not very well explained. All I hear is "use this" but there is no one telling you why, or why not. And how to actually implement it beside the tutorials. Even with docs auth0 seemed very confusing, especially when it's uncertain on what user info I actually get from it...