Previous convictions

Questions:

• How long do I need to disclose my conviction for?
• I have been given a penalty notice for disorder, does that mean I have got a criminal conviction?
• I want to travel to America but I have a conviction/been arrested. Can I still travel there?
• The police hold personal data about me on their systems that is inaccurate, how can I get this corrected or erased?
• What is a caution and how long does it last?