Welding problems

• Why choosing brazing?
• What's the recommended joint clearance?
• What's capillary flow?
• Is silver content in brazing alloy expensive? 
• Why using flux when brazing? 
• Why do the Copper - Phosphorus alloys need no flux for copper to copper brazing? 
• What should the selecting criterion be for choosing a brazing filler metal?
• How can I reach the brazing temperature? 
• What are the advantages of a brazing filler metal flexi flux coated?
• What's brazing temperature? 
• What's necessary for successful brazing?