The difference between kicking tees and normal cones is that generally tees are more accuarate. That's why I, personally, use them when i kick for my team.
When the opposing team gives away a penalty, and the team who won the penalty chooses to have a kick at goal. They get three points if it goes over. Or if a team scores a try, they have to try and convert it anywhere in line of where the ball was touched down. They get two points if it goes over.