All Quiet on the Western Front to re-read. *(They can be had on amazon for pennies, plus shipping.) There is a very informative series of videos on youtube that can get you caught up on all the minutiae of WWI, and there are a great many historical novels that can do the same. These overarching narratives will talk at length about troop movements, and shells fired, and lives lost. So many lives lost. Too many to count. It was a nightmare beyond reckoning.
Through all that numbing information the actual cost and consequences of the war get lost. It's all well and good to know that the troops were in one place or another, but what where they doing? All Quiet On the Western Front makes an effort to bring that to light. It is a superb book that is just as thoroughly modern and relevant today as it was the day it was published in 1929.
Mostly they were trying to kill other people, at which they excelled, and also they were trying not to die, at which they did not.
The book itself is a slim volume that can be read through in a few sittings, if you have the stomach for it. More likely you will have to read it in smaller sections, as the wretched misery of trench warfare in 1916 is only occasionally interrupted by 'happy' moments.
If you read only one book about WWI, or only one book about war in general, then this is the book to read.