Help with Gold Trading

Hi,

I'm interested in testing the water with investing in gold trading but have very little knowledge in this area and am hoping someone can provide some insight into the basics from a newbie perspective.

Things i'd like to know are:

• Minimum investment?
  
• Recommended sites
  
• Gold measurements/quantities traded in?
  
• Web trading only or can you use App or over the phone?
  
• What is long and short trading?
  
• what is the general process?
  

Any help appreciated!
Thanks