Tamara
Product-Market Fit
Before we start with the product development, let's look at two different types of validation: market validation and product validation. In the end, you want to achieve something called a "Product-Market Fit".

What are Market & Product Validation and Product-Market Fit?
Market Validation takes care of proving that a certain target group has a need that needs to be solved.
Product Validation takes care of developing the best possible product, features and UX design that will bring value and customers will like.
Finally, a Product-Market Fit is defined by Marc Andreessen as:
Product-market fit means being in a good market with a product that can satisfy that market.
Dan Olsen further explains Product-Market Fit as an alignment between the Target Customer, the Underserved Need, the Value Proposition, the Feature Set and the UX.

Why is Product-Market Fit important?
Product-Market fit is important because you want to play in an attractive market with the best possible product.
How to create a Product-Market Fit?
A product-market fit is usually achieved by following an incremental, lean startup approach where you define hypotheses, test them with the next minimum investment and iterate your assumptions, just as we've done so far. Each time, you can improve your assumptions and build more advanced solutions.
The market validation comes from a general interest and potentially willingness to pay for your solution coming from target customers. Such validations can be achieved by setting up a landing page or website, running ads, conducting sales or other methods in which customers would demonstrate their interest through an action (sign-up, purchase...).
Product validation comes more from observations of, discussions with and feedback from users using your product. At a first stage, this can be a prototype, that later develops into an MVP and gets better and better with time.
Supporting Tools & Additional Resources
Book: "The Lean Product Playbook: How to Innovation with Minimum Viable Products and Rapid Customer Feedback", by Dan Olsen
Let's look in more details into product and market validation, prototypes, websites and MVPs in the following articles.