The introduction section is the shortest. Start out with a Cover Letter and a Title Page. Keep the Cover Letter brief: simply write a personal introduction to explain who you are and provide your contact information. The Title Page should be exactly what it sounds like: a title that introduces your proposal and provides a clear message about the ideas and/or services you are pitching. Some examples might be "Proposal to Create a New Executive Assistant Position", "Proposed Temporary Services to Benefit the Stuart Corporation", "Executive Search Services Proposed for Jameson Company", or "Suggested Candidates for the Vice President Position".
You can look online for sample proposals that you can work from, in many cases you will be able to download a template that you can work from. You will most likely find that there are dozens of sites offering hundreds of different templates to download. It may take a while, but you will find that there proposal forms that will match almost any need including yours. Take your time and select the one that best suits your needs.