It is the narrative of the “ask” — the justification as to why law enforcement believes that fruits of a specified crime will be found in a particular place. There must be probable cause — that is a “fair probability” why law enforcement believes fruits of a crime will be discovered in the place to be searched. Probable cause requires some level of corroboration to match what the informants provide.
The search warrant is the cover sheet, — what the judge signs to authorize the search and articulate the scope of the search.
But, regarding sealing and unsealing a search warrant, the search warrant and the affidavit go hand in hand.