In the module, "Approve Records from a Chatter Feed", when creating an Approval process, you cannot complete the exercise because the user "Allison Wheeler" does not exist.  The user needs to first be created before they can be added as an approved, otherwise you cannot continue with the exercise or save the Approval Process.

In the Specify Entry Criteria section, set up the criteria the record must meet to kick off this approval process.
In our example, we want Allison Wheeler to approve any accounts that she doesn’t own, so we enter these criteria on the first line.
Field: Account: Account Owner
Operator: not equal to
Value: Allison Wheeler
In the Select Approver section, assign all approval requests to Allison Wheeler.
Select Automatically assign to approver(s).

I get the error; "you must enter a value" for Allison.  What's wrong?
Select User, and, in the second field, enter Allison Wheeler.

In the module, "Approve Records from a Chatter Feed", when creating an Approval process, you cannot complete the exercise because the user "Allison Wheeler" does not exist.  The user needs to first be created before they can be added as an approved, otherwise you cannot continue with the exercise or save the Approval Process.