Steps are fields which determine how long a job takes and when it has been started or completed.
Steps are generally the field where you would enter a customer's address - but this isn't mandatory.
Custom Fields are places where you can enter extra information about a job.
Use Custom fields to create a field to add Notes or additional information that you need, like progress or status.
You can use Pick Lists to setup pre defined selections.
You can make this field optional for workers to use when they need.