What is the first stage in the new product process?

Idea, design, prototype. Depending on the cost and complexity of the design and the cost of the prototype, somewhere after the idea is drafted and a preliminary design completed, you'd do market research to validate the feasibility of producing and selling the product, looking at things like: market size, time and cost to produce and distribute, product price, sales model and distribution channels, production and materials costs, marketing costs, competitive landscape.