You can easily reach Paris downtown and the congress centre from any of the three airports that serve Paris:
You can also reach Paris by train and arrive at any of its 7 stations. More information can be found here.
To reach the Congress Centre, an easy way is to take the metro. The station "Porte Maillot" is located right in front of the congress centre.
You can plan your journey from your hotel or from the airport to the congress centre here.
Here is a map where you can get directions to reach the Paris Congress Centre (Palais des congrés):
Address: 2, place de la Porte Maillot - 75017 Paris