Dear Keerthana,
Entering into the business agreement is the culmination. Generally, the purchaser identifies the potential service providers and sends the "Request for Proposal" (RFP). In reply, the service provider submits either a business proposal or a quotation. Thereafter, the negotiations take place and the agreement is made.
However, we the members of this forum are not aware of the nature of the business of your company, the type of services provided by the service provider and what terms and conditions were negotiated during the negotiation. Sans this information, it would be difficult to provide any suggestions.
Since your company will be the purchaser of the services, you may issue the Purchase Order (PO) to the service provider. In the PO, you may mention the terms and conditions. In the terms and conditions, you can outline how the orders will be communicated, how the orders will be numbered, what will be the pricing structure for the various services, how the quality of the work will be measured, delivery terms of the services, payment terms, method of raising the invoice and so on. The PO on the company letterhead is a valid document and acts as a business agreement. However, let the PO be signed by the MD of your company and no one else.
Thanks,
Dinesh Divekar