Click here for the link to Gospel Principles Lesson #1: Our Father in Heaven lesson from the manual.
The great thing about these Gospel Principles lessons is that there is all kinds of helpful information if you are looking for further study. Mormon.org is a great place to start as it contains all our basic beliefs as well as links to more articles.
"God is Our Father"- This is a video that briefly explains our relationship to our Heavenly Father
"The Grandeur of God" by Elder Jeffrey R. Holland (of the Quorum of the 12 apostles)- How Jesus clarifies God's role for us.
"Knowing God" by Elder Bernard P. Brockbank (Assistant to the Council of the 12, July 1972)- Again, coming to know God involves coming to know Jesus and His teachings.
These next few are from Mormon.org and directly answer the questions the manual asks so its a great place to point people if they have additional questions as well as a place to study for your own answers.
What are some of things that tell you there is a God?
What do Mormons believe about the nature of God?
How can we come to know our Father in Heaven?