Pick the topics that are most relevant to you and slowly work through them.
You will find a wealth of information and numerical data in this guide, and I recommend you go through it section by section. Heading into Shadowlands, this guide will serve the same purpose as it did in BfA and prior expansions: providing quality and accurate information about Retribution Paladin. I have been raiding Mythic progression for a long time, and I have played a Retribution Paladin as my main for even longer.
I am a Ret Moderator/Theorycrafter/Templar in the Hammer of Wrath Paladin Discord, and you can check me out in-game under the name Ilivath.