What do these two sentences mean?
Ich soll das Buch lesen.
Ich sollte das Buch lesen.
I have mostly seen "should" translated as "sollte", but that seems to be past tense. The first one would be "I should read the book." and the second one "I should have read the book."
I believe this is incorrect, however. What is the proper use of this verb? What is the difference between "ich soll", "ich solle", and "ich sollte"?