Content Confusion

As  I progress farther along in my studies to become a teacher, I'm finding it more and more difficult to come up with lesson plans. I don't have trouble for the simple fact of coming up with creative ideas. Its the fact that I feel lost as to what exactly I am supposed to be teaching. Am I missing something? How are we to know what we are supposed to be teaching? In my observations we are currently reading The Diary of Anne Frank. My question is not what are we supposed to teach in regards to the text, but how was it decided that we were to read THAT certain text. Are we told this by team leaders? I have yet to have this question answered. Even though it seems to be such a simple answer. This is why when I sit down to create a lesson plan, it becomes difficult because I don't have a basis to go off of.  Standards only get you so far. Standards don't provide what texts I should be teaching. Can anyone answer such a simple question?