The introduction should lay out the scope of the document. The first sentence should show what the reader will be aware after having finally read the document.

The second sentence should describe the essential points of the document

1. terms and concepts which may require an understanding before reading other sections
2. the current situation
3. the proposal

The third sentence defines the scope by describing what the document will not do.

To emphasis the scope of the document there are two subheadings

1. Intended Audience
2. Project Vision

A Word example for this section can be found here. Change the text XxProspectxx to the name of the client.