Keep in mind that you are actually asking for the summary of an epic poem, which is quite an unusual request. However, I am happy to provide one for you. Also, you didn't indicate whether you wanted the summary in Spanish or English. Since eNotes is primarily an English-language site, I am going to use that language. Regardless, this story is about the native culture of Chile during Spain's attempt to conquer Chile under Alonso de Ercilla.
As the national poem of Chile and a work of the Spanish Golden Age, this story is mostly about numerous battles. The Arauca Indians were both a fierce and a proud race to take on the Spanish. A member of Phillip II's own family tells that story. All the Arauca want is independence, but it doesn't come easily.
As evidenced by the story, the full fight became known as the Arauco War. We learn that this story is really about just the beginning of that war. Now we read, in verse form, battle after battle of the lesser-known conqusest of this war precisely because the author fought in them and could give first hand experience. The result would affect Chile economically, socially, and politically for centuries.
In conclusion, please realize that La Araucana is known as The Araucaniad when it is referred to in English. Due to the discrepancies in translation and due to the fact that it is a 16th-century epic poem, summaries are hard to come by.