You can only smoke marijuana on private property because it is still federally illegal. Therefore, you may not smoke it on federal grounds including parks or on the street.
If you smoke marijuana publicly, you are subject to legal charges and fines. Also private buildings (such as apartment complexes) may have their own rule about marijuana usage and you must comply.
You are allowed to smoke marijuana on private property only. Be sure to check how much you are legally allowed to possess at a time. In public, you can possess a certain amount of marijuana, but it is illegal to use it. Should you use it on public grounds/federal property, you are subject to legal charges and fines.