Any ID I could reference in sections I created a section for appointment record (channel type). Each appointment record has different fields, i.e. customer name, phone#, address, etc... I would like to set a unique appointment_record_id (Numeric, i.e. 234) for each record.  Is there any way to create it?
If you were to do this on entry save, it'd be much easier/cleaner.

You'd write a simple plugin that listened to the onBeforeSaveEntry event.

The plugin would check the isNewEntry param to make this this is a new entry and not an existing one.

If it's new, you could generate a random numeric value with mt_rand, assign it to your custom field and left the request continue so Craft can save it to the entry.

A string field for the unique identifier would be better though, since mt_rand will not always produce unique numbers (for unique numbers you'd need to keep a separate database table and obtain id's within a transaction). If you'd use strings you could use uniqid('', true) if you deploy on a single server, or better use a uuid/guid.

If you didn't do it on save, but wanted to be auto-populated when someone clicked "New Entry", you'd have to do something much more hacky like have JS loaded load, try to target the field in the particular section with JavaScript and inject the random number into the DOM.