Could I recommend you read the responses already given, and look up the links provided, before asking questions to which people have already given you answers, or ways of finding out the answers?
I gave you the link to viamichelin to work out the route from France - all you have to do is enter Calais as departure point and Brussels as arrival point and then if you wish, adjust (which you can do by focussing on the map) for the RING EXIT that I also gave you!
AND I gave you a link to the Brussels Expo site, to a page with at least 5 maps indicating access to that area by road, from European to city to local level - on the most local of which, in the bottom left-hand corner, the Atomium, Expo buildings and metro station (M) are all identified, together with STREET NAMES!!!
I also referred to "the CAR PARK by the Atomium" - in fact, it's between the Expo buildings and the Atomium, alongside the tram/metro line, although there is also parking along some of the roads illustrated, as well as car parks you would have to pay for next to the Expo buildings. Heysel is a metro station and an area, it doesn't have an exact address but is on Avenue de l'Impératrice Charlotte/ Kaizerin Charlottelaan. The car park (which serves the Atomium, Kinepolis cinema and Bruparck) is an open space to the South (left on map) of Boulevard du Centenaire/ Eeuwfeestlaan. You are not likely to miss the Atomium, and once you get to that area you will soon see where cars are parked.