In the main arena there is just the gun site. Off-line and in the training arenas there is a "lead computing site" you can use to see how much you have to lead.
To turn on the lead computing gun site off line, launch the game and go to "off line practice".
Then go to options/arena settings/environment/arena settings.
Then under the General tab scroll down and double click "Flight mode tags".
On that list scroll down to "lead computing site and click the box next to it.
The click "OK" and then "Save" and your set.
To use the site , once in the air hit the tab button to highlight the closest plane. As you dive in on the plane you'll see 2 green plus signs. This where your primary gun and secondary gun will hit. Put your site pipper (center dot of the site) on the green plusses and you will score hits.
There are a number of different site available and you can change them from the clipboard.
If you want, film your flights and send them to me and Ill look at them and give you some pointers on what you might be doing wrong.
Good Luck