How do you I make a manpower services business proposal to clients, it's format and contents?

Is this a proposal or introductory letter? A proposal is for bidding, an introduction letter is for generating contacts and leads. We have no idea what you are planning. For an introduction, just tell them your background and what services you can or have provided and what your charges are. For a proposal, you will need to tell them what you propose to do and how much it will cost.