This war is separate into two part first part going to watch in 2018 and the second part will be coming in the year of 2019 with the name of endgame.
In the first part thanos as a villain having a goal to collect all infinity stone present in universe by the purpose he send its army to earth for collecting the stones.
Thanos army meet the iron man and Dr. Strange. They compete with the army but failed and the army decided to go in thier planet ( titan) where they met with guardians of galaxy.
In the earth where other avengers like captain america, black widow, banner, black panther, vision are dealing with the army of thanos.
But later on they realised that they are not able to compete with them.
But no! The god of thunder, yes THOR is come with thier new weapon strombreaker. The fight of thor and thanos army is really awesome
Thanos come in the earth to take the vision's stone. With the help of time stone he is able to go in past and collect the time stone.
Overall all the characters played an amazed role in infinity war except hulk I think so.