Description
The 'User in Field' check will verify that the current user is in the specified field, typically a multi-select/user picker custom field.
Configuration
You must specify the field that is the prerequisite for this transition, and whether the user must be in the field or not, when configuring the check. For example:
Example
A workflow is configured so that the 'Approve' transition has the 'User in Field' check. If the current user is not the specified reviewer, the description will be modified to show who performed the review instead.