At this point, we hope you get how the restricted plane works, but you may have questions like, "How do I know how thick the restricted plane is?", "How do I know what direction the restricted plane extends from a mando object?", or "On something like a tree with multiple branches, where does the restricted plane start?".
Those are all excellent questions, but if you're playing a tournament, the only person who can answer them is a TD. The 2022 PDGA rule updates left it entirely up to TDs to define restricted plane for any mandatory. For example, an event's caddie book could say, "On hole 14, the first big pine tree is a mandatory object. Seen from the tee, the restricted plane starts from the farthest left point of the tree's main trunk and extends infinitely right and upward. There is string to the right of the mandatory indicating the direction in which the restricted plane extends from the tree's trunk. The string also defines the thickness of the restricted plane."
As you can tell from that example, TDs have to be extremely detailed in their rule descriptions and course setups when they include mandos. If you have questions about a mando before playing a tournament and can't find the resources to answer them, you should contact the TD or ask your questions in the players' meeting before the round begins.
If you're playing a casual round and a course has a mando that isn't well-defined, just use your best judgement to decide what direction and thickness of the restricted plane makes the most sense.