"How To Be A Pandas Expert"[1] is a good primer on dataframes. There's a certain mental model you need to use dataframes effectively but it's not apparent from reading the official docs. The video makes it explicit: dataframes are about like-indexed one-dimensional data, and every dataframe operation can be understood in terms of what it does to the index.

[1] https://www.youtube.com/watch?v=oazUQPrs8nw