Here's a little visual to add to what John said.



Just as an FYI, there are actually 4 Modes that are used in transmitters. Here is a quick rundown of what those entail.



As has been said already, most of the US goes to Mode 2. Although you can go either way. Many of the radio systems today can be changed by the user from Mode 1 to Mode 2. But the biggest thing to consider is that going to Mode one can isolate you from help from other people, most importantly is your trainer. Going Mode 1 could make it hard for them to buddy box you, or even take the radio over if you get in trouble.

Hope this helps

Ken