When you decide to create a new product, whether it is a new website or a mobile app, you should consider defining a minimum set of features that you can launch the product with and that will deliver value to your customers, and this set is refer to it as the Minimum Viable Product (MVP). In other words, the MVP should include the smallest possible set of features that enables the users to use your product without any issues and delivers them the value they are seeking.
For example, if you want to launch an e-commerce website then this set will include things like the product catalogs, shopping cart, ability to place orders, ability to accept payment, ability to create user accounts, and many other.
In addition to the features set, you need to define the platform you will launch the product on. For example, if the product was a mobile application then is it going to be native app, web app, or a hybrid? If it was a website, what are there certain features that are not supported by certain browsers?
Defining the MVP will help you determine the cost needed to launch the product, as well as how long this MVP will take to be developed and tested.