First, you need to find out of your are eligible Seniors, families with a disabled member and families with children are given preference in this program. The government provides this state-by-state guide (PDF). Look it over and see if you are eligible.
Each state runs it's own program. You will have to find the office in your state. Go into the office. Fill out a form answer some questions and if you are eligible, they will send experts to make your home energy efficient.