A form displays one record. Its fields have types and rules: a reference points to another record, a choice stores a selected value, and a mandatory field must contain a value before a valid save. Use the reference picker to select the intended person rather than relying on a similar display name.
A read-only field can't be changed through ordinary form editing. Number identifies an incident for people and is read only in this instance. Short description and Caller are required. A blank Assigned to field is allowed, because a group can own a queue before an individual accepts the task. Review these differences before filling every blank. Mandatory fields describe data requirements; they don't automatically grant permission to view or change the record.