They are completely different disease. The flu hits much harder and faster. Symptoms include fever, chills, major body aches and a dry hacking cough. You'll recover from a simple cold in about a week but the worst symptoms should be improved in 3 to 5 days. The flu can last longer, at least 7 to 10 days.
Hand washing is the simplest, most effective way to keep from catching a cold.
Cold viruses can linger for hours on skin or commonly used objects, such as coffee cups and door knobs. The longer you spend with someone who has a cold or the flu, the greater the chances of catching it yourself. See Influenza for more information on the flu or Viral Upper Respiratory Infections for colds.