Please refer to the guide on Azure DevOps - Customising the Work Item Form
Select "User Story" for the work item type.
Page 1 - Details
Page 2 - Concept Design
The Control extension is the Multivalue Control Extension that allows the user to select multiple items from a picklist:
Multivalue control - Visual Studio Marketplace
For adding a new state, please refer to Azure DevOps - Adding or editing custom states
