Diagrams are a definite help when watching Tenet. It's sort of a time travel movie.
But people don't just teleport to the time period they want to go to like in a typical time travel movie.
Rather, people change the direction that they go through time, but they flow through time at the same rate.
That probably doesn't make sense, but I think an example can clarify the concept.
Let's say two people going opposite directions through time pass each other on New Years Eve 1995.
After living for a year, the guy going forward in time will reach New Years Eve 1996.
After living for a year, the guy going backwards in time will reach New Years Eve 1994.
So if you want to go backwards in time to 50 years ago, you have to actually live for 50 years while you are going backwards in time, watching the world slowly unwind like a movie being played backwards.
If you get in a gun fight with someone going the opposite direction through time as you're currently going, the first thing you see are bullet holes. Then you see bullets leaping from those holes and into the gun of the guy who is shooting at you.
From his perspective he is firing the gun at you. From your perspective he is unfiring
So anyway, they have some complicated battles where both sides can come back and participate in the same fight over and over again by reversing their direction through time after the battle is over. Some of the people in the fight are doing everything normally, and others in the fight are doing everything backwards. And some of the people in the fight are actually the same person.
And since the main character also takes multiple passes at some of these fights, some of the fights you get to see run through from both directions, and from different perspectives because he is in a different spot each time he goes back into the battle.
It's these complicated battles that people are making diagrams to explain.