I don't really understand the graphs in Premiere

https://preview.redd.it/m10zy1jgjmif1.png?width=701&format=png&auto=webp&s=d7b9c9b97d20a1c4e3c931c0b1ba44475615cd35

Is there any tutorial explaining why some properties have these two graphs and some have one, why some keyframe handles can only be extended vertically or dragged up or down from the same position but other keyframe handles change in direction/angle? I learnt they're the value and speed graphs, but I've not really gotten the hang of it, and sometimes I can't tell what I'm changing. Thanks