NO, it does not hurt but you may feel little discomfort. 

• Avoid consuming sticky foods (chewing gums, toffees, etc), hard foods (Ice, nuts, bagels, chips, etc), sugary foods which can decline your teeth health.
• Do not bite your nails, or chew pencils, pen or any other objects.
• Use lukewarm salt-water to gurgle if you feel pain and soreness.
• Brush your teeth at least 3 times a day.
• Use floss and mouthwash
• Regularly check your braces for bent or loose wires and brackets.
• When you take out your retainer to eat, make sure you brush your teeth, floss, and remember to keep your retainer safe and keep your retainer clean by brushing it gently with a toothbrush and toothpaste. You may also soak it in denture cleaner. Do not put your retainer in boiling water or in the dishwasher.

• skipping visits or no visit to dentist when called
• wire breaks (eating hard food)
• not brushing properly or no flossing

Duration varies from purpose of wearing the braces. Generally 1-1.5 years.

Yes, atleast 3 times a day you should brush to make sure that no food is suck in the braces.

And you must use floss daily too.

A retainer is a custom made device used after an orthodontic treatment, in order to make the tooth settle to it’s new positions and the gums might get well adjusted to them. It is necessary as it helps the gums to adjust to the changes in the bone.