Questions about the Harry Potter saga? I havent read Deathly Hallows yet but i know what happens?

You answered your own first question: yes, Slytherine created the Chamber of Secrets to house the basalisc in a descrete way so he could kill the muggle borns at Hogwarts. I don't really know the importance of the Deathly Hallows, but yes they do make you the master of death. Voldemort was raised in a non-magical household, so he was never read the tle of the three brothers, so he didn't know about the cloak of invisibility or the resurrection stone. He only wanted the elder wand so he could kill Harry. At the end of book 5, it is said that Dumbledor walked into the Forbidden Forest and retrieved Umbridge from the Centaurs, but thats all I know that happened to her. Although Lucius Malfoy was imprisioned, Voldemort broke all of his followers out of Azkaban over the summer before Harry's 17th birthday in Deathly Hallows.