Think the best place to start is understanding that renpy is programmed in python and for the most part renpy script is just a simplification/extension of python. For the most part you can actually write your entire game in either renpy script or python, or a combination, and it would not matter much. While knowing python would be extremely helpful for an advanced game or or one that intends to get away from a visual novel. For the most part, to make a basic games knowing python is probably unnecessary to make a visual novel or game.
While i did know how to code before i made my first renpy game, i did not know python and actually just learned renpy script by the included demo/tutorial in the sdk. They even include a tutorial on making pong in the renpy visual novel engine, to demonstrate that while the script was built for visual novels, sky’s the limit if you know some python and get creative. Also by reading the fairly complete documentation for renpy script on the renpy.org page.
Renpy script uses if then else statements along with labels for flow control. along with direct python variables for all tracked variables. If you can make a flow diagram for your story or game, with decision branching, then each block between the decision points is a label, and you just have your variables you track stats or decisions with that you use in the if then statements to decide which label to execute next.
In summary i would start with the demo/tutorial in the sdk, with the renpy.org page used to find lots of the nitty gritty details needed as you get more advanced. Also would read this Some notes about RenPy by @dingotush who has some helpfull pointers on quirks of renpy