After you've defined the problem and designed a solution, it's time to build it. Depending on the nature of the product you are working on, development and deployment durations could vary a lot. Web/mobile apps deploy quickly, while hardware might take a long time between the product's design and when it's actually ready for mass production.

Building the Solution is Step 3.

• Translate the design to a real product.
• Software may use lean development with frequent releases of incremental builds.
• Hardware typically have fewer releases of more substantial changes.
• Product Managers may encourage, prioritize and help (Usually, not physically writing code or designing circuits).

The product development life cycle isn't linear, it's usually iterative, especially between design and building the solution. Common cases are usually identified at the design stage, but edge cases might prop up while engineering is building the product. At this stage, prototypes are shared to customers/stakeholders to get early feedback about the product.

Does it effectively meet the customers' needs? Or is there a big tradeoff you did not anticipate? If an MVP is built, you can start testing the core product. Feedback should be garnered at the right time and in many phases. The development phase is done when a working product has been thoroughly tested and is ready for release.