User flow is the standard path taken by a user on your website in order for them to complete a certain task
User flow deals with a lot of UX (user experience) and UI (user interface). It is the journey a typical user will take while on your website in order to achieve their goal. A simple, sensible user flow can drastically increase conversion rates while a difficult and hard to navigate user flow will seriously hinder growth. An example of a standard and simple user flow could be: the home page, to a free trial start, to the account dashboard, to the purchase page, and finally to the payment page. This user flow allowed the user to see what your product was via the home page, try the product for free, see what a paid account would look like, view the pricing, and finally purchase. A general rule of thumb is a user should not have to make any more than 3 clicks on a website when trying to access a certain page.