Institute of Supply Management (ISM) explains the difference between procurement and purchasing:
Procurement is an organizational function that includes specifications development, value analysis, supplier market research, negotiation, buying activities, contract administration, inventory control, traffic, receiving and stores. Purchasing refers to the major function of an organization that is responsible for acquisition of required materials, services and equipment.
Examples of RFPs, RFQs, ITB or contracts for various products and services are frequently posted on local government websites. Use Google to search for document samples:
Oracle ERP RFP site:.gov
HVAC "statement of work" site:.gov
In order to understand how the price of a good or service is determined, need to understand the composition of a good or service. In contract negotiations, this knowledge helps deliver a fairer price.