You just simply go near a thing that you cannot climb onto if you want to climb on that thing it should be normal height's. (just as big as you can climb on) now talk to Ron or Hermonie and when the talk is over you will be on that thing (i haven't completed the game so i don't know if it works with Sirius or Dumbledore).
Note: You will need Incendio to do this
Find a gargoyle and cast Incendio on it. Fire will come out of it's nose if you aimed well. It will also give you secrets.
Talk to the Gifford Abbot (Floor 1, Grand Staircase) then talk to a Hufflepuff student. The password is "Dragon's egg".