The Iliad is a description of 24 days of the 10 year war. It does not start at the beginning nor does it include the end.

It starts when the Trojan war has already gone on for 9 years. My copy begins with "The wrath of Achilles is my theme." 

A plague breaks out. Achilles, the best fighter, calls an assembly. The sooth-sayer types say that Agamemnon, the head guy, needs to give the girl Cryseis back to her father. Agamemnon takes this as a threat and so, to maintain his reputation as one tough dude, he takes Briseis away from Achilles to make up for his loss of Cryseis. Achilles is going to kill Agamemnon on the spot but is stopped by divine intervention (Athena). Instead, Achilles withdraws his services and watches the Greeks suffer from a lack of his services, that is enjoys watching them being slaughtered because he is really angry and not very nice.

Things get worse and worse for the Greeks. Zeus is honoring a promise to Thetis, Achilles' Goddess mother, to make Agamemnon (and thus the Greeks) suffer for the indignity. Finally, the Greeks are in really bad shape with the Trojans right at the ships and most of the best Greek warriors are wounded. Hector, the top Trojan warrior kills Patroclus (sp?) who is Achilles' best friend. Achilles is mad at the Trojans now and so he joins in with the Greeks and this shifts the balance to the Greeks. They kill all kinds of Trojans and the Trojans are now on the run and hide inside this city.

Achilles, still completely angry about Patroclus, goes outside of the gates of Troy, alone, and calls to Hector to fight him one on one. He doesn't give up but keeps calling out. Eventually Hector does this out of honor. Achilles kills Hector. Still completely consumed by anger, he ties the body of Hector to his chariot and drags it around a whole bunch. Finally, an envoy is sent by Priam, the king of Troy, to negotiate to get the body of Hector, his son, back for proper funeral rights. Priam and Achilles meet in the area...