Pausch wants to help people achieve their dreams, so he explains how he achieved his own dreams. Pausch uses a central idea and supporting detail structure so he can talk about several different examples that connect to the central idea of achieving dreams and goals. He ends his lecture by explaining what lessons can be learned from his experiences so that other people can also fulfill their dreams and help others do the same.

what part do you need with?

the pronoun reference replaces a noun, but you have to make sure there's no room for confusion.

in the first sentence "her" could be referring to shely or to the sister. the answer there is "shelly called her sister and told her about the new baby."

in the second sentence "it" could be referring to the roof or the floor. the answer there is "since the roof leaks on the family room floor, we need to repair the roof."

whatever is after like is what is being compared they are comparing bumping into you like they are scared to catch germs you have and to you being contagious