Writing each feature of your app as a user story is a great way to break down the work into smaller pieces. Developers can then write specific tasks that need to take place in order to make that user story true.

Here is the format you should use when writing a user story:

As a { type of user }, I want { some goal } so that { some reason }.

Examples

Login functionality for a marketing app:

As a marketing user, I want to be able to enter an email address and password so that I can access my marketing team account.

Additional Resources

Atlassian / Jira have their own definition :

A user story is the smallest unit of work in an agile framework. It’s an end goal, not a feature, expressed from the software user’s perspective.

The purpose of a user story is articulate how a piece of work will deliver a particular value back to the customer. Note that “customers” don’t have to be external end users in the traditional sense, they can also be internal customers or colleagues within your organization who depend on your team.

User stories are a few sentences in simple language that outline the desired outcome. They don’t go into detail. Requirements are added later, once agreed upon by the team.

– Atlassian / Jira

Some other great resources