Azure DevOps Scrum project sprint work process not being updated

I have a Scrum project in my Azure DevOps Server. I assigned an effort to each PBI and set the capacity for each user. I see in the right panel Work details the hours for each activity.

1. How do I mark a Task or PBI that its "Testing" or "Documentation"?
2. Even though I marked many PBIs as "Done", all the times are still 0 of X h. Why don't they change according to the effort?

The activities ("Testing" or "Documentation" etc.) are a field with drop-down list - Microsoft.VSTS.Common.Activity, you need to add to your PBI/Task layout and choose the activity.

To change the Activity menu selections, see Add or modify a field, customize a picklist.

Even you move PBI/Task to Done the remaining work not changed to 0 automatically. to achieve that you need to make a custom rule. if you still working with hosted XML process it's something like that:

<STATE value="Done">
  <FIELDS>
    <FIELD refname="Microsoft.VSTS.Scheduling.RemainingWork">
      <WHEN field="System.Reason" value="Completed">
        <COPY from="value" value="0" />
      </WHEN>
    </FIELD>
  </FIELDS>
</STATE>