In the exposition we are first introduced to Thor, Loki, and Thanos.Thanos has come to steal the space stone from Thor to complete one of his main missions.While doing that, Thanos kills all the asgardians including his brother Loki.
In the rising action Bruce comes to warn Tony and Doctor Strange of whats to come and what danger they all are in.So Tony decides to get help from Steve and the others.
Also in the rising action Steve and the others have come to Wakanda to hopefully get the mind stone out of Vision and to protect him from Thanos and any other threats.
The climax is that Thanos has just arrived to Wakanda and had successfullly retrieved the time stone from Doctor Strange and now Thanos has come to get his final stone from Vision.
The falling action is that Thanos had successfully got the mind stone from Vision and has defeated everyone who was trying to stop him but he finally finished what he was trying to do which was to wipe out everyone with the snap of his finger.
In the resolution, after Thanos snapped his finger and teleported somewhere else most people started to disapear and that left everyone in surprise and wondering what to do after Thanos had just defeated them.