we are looking at the metro/rer map and i have read that you can take the rer a(red) to vincennes but how do we catch the metro 1(yellow)? on the map they do not intersect.
You have to complete that transfer on foot, walking ground-level (9 minutes) from Vincennes RER A to Chateau de Vincennes Metro line 1. Note that if you're not using a pass you'll need multiple tickets to make that transfer. In this case you'd buy a RER ticket from Marne la Vallee to Vincennes, then use a Paris Metro ticket at Chateau de Vincennes to anywhere in Paris Zone 1.