This can be due to many things.
The first thing that many new users of Nitro Cars need to know is that a Glow Plug Igniter is needed. The Glow Plug Igniter must be fully charged prior to attaching it to the glow plug. If it is fully charged and it is attached to the Glow Plug. Make sure a good connection is made.
Second, if the above is done you should check to make sure that fuel is getting to the carburetor. This can easily be done by holding your finger over the exhaust hole and giving a few pulls on the pull start. This will cause fuel to siphon through the fuel line to the Carburetor. Make sure that you do not pull the pull cord all the way to the end. Starting is a learned art and can easily be done with short quick pulls about 1/2 of the way.
Third, if the above two do not resolve the starting issue, you may have flooded the engine. You can remove the glow plug and turn the car upside down and pull the cord a few times to clear out the fuel than restart.
Lastly, your settings may be mis adjusted.