The racing line is the route a racing driver follows in order to take corners in the fastest possible way. By using all of the available space on the track, cars can travel in a straighter line and travel faster before reaching the limits of tire grip.
The experienced drivers have a general sense of where the racing line is for the track conditions and their car's idiosyncrasies and with each lap they are striving to find that perfect line. Until they come up on a noob in their way.
Chances are as noob, you are too busy trying to get comfortable in your new, cramped, just barely finished the final touches on the car right before race time, cobbled together powerwheels, to have any wherewithal to even think of hitting the racing line. At least during the first sprint of the day.
Below are a few articles worth reading and the thing to keep in mind most during your first race is really to try to stay out of the racing line as a courtesy to the more seasoned drivers. Especially if you have a slower car that has staked it's winning strategy on scoring moxie points.
Don't like to read? Watch this video! https://www.youtube.com/watch?v=VEJh4lLCzRc