I already guessed all the 10 chapters at the beginning but it doesn't show an example of that function ( srcrect).
Indeed no example, but it is being discussed in the accompanied text.
It's pretty simple. You can give RenderCopy() both a source as well as a destination rectangle (another question you had in the thread linked by Carver413).
The srcrect parameter is the rectangle it needs to copy from your image. The rectangle is given in pixels, and i am assuming that you know where your first and your second car are located (pixel-wise) inside the image.
The example where Carver413 pointed to, shows how you can provide a rectangle. The only thing left for you to do is storing the correct x/y coordinates as well as correct width and height inside the rectangle and provide that to RenderCopy()'s srcrect parameter.