how to consume 50gb free cloud storage offered while buying mac air.

MrHoffman wrote:

There is free iCloud storage available temporarily, during the purchase and data transfer.

I wonder if this is what the original poster means.

• I believe this storage is available regardless of whether purchasing AppleCare.
• I have never seen any limit on the temporary storage quantity offered.

There is free iCloud storage available temporarily, during the purchase and data transfer.

That iCloud storage is available for three weeks, and then disappears.

Details: Get temporary iCloud storage when you buy a new iPhone or iPad - Apple Support

You may store plenty of data in iCloud. Examples are photos, videos, calendars, contacts, notes.

See this.

iCloud User Guide - Apple Support