Okra-shrimp Gumbo

• 4 stalks celery
• 2 boxes okra (frozen)
• 1 1/2 cook spoons flour (plain)
• 1 onion
• 1/2 bell pepper
• 750 gr shrimp
• 270 gr salty oysters
• 34 gr shallots
• 30 ml cooking oil
• 1 package tomatoes (whole)