To make them, its called making 'new layouts'
to do this u need to of unlocked s2
then load up the track u want to edit/add objects, and the 'race'/'go'
once loaded, press shift + u, then space to bring up the menu/s, and click 'place objects' to 'on' at the bottom left hand corner.
when you have done that u can see icons top right of your screen. also the key commands top left (u have to press a certain key to place an object)
and thats it...