Hi there.
While creating a race map, you need to go to "Map settings " (on the map editor) and go to "Gamemodes".
Then, add the "race" gamemode.
After that, you save the chances, and you scroll the objects/car/marker bar to create race objects.
More info, feel free to ask me again.
EDIT: If you create a marker (without race mode) you can left click and go where it says "Cylinder", and change it to "Checkpoint".
How ever, its not the same, you need race gamemode.