In the original question (before our editing) you asked if you need a transit visa to leave the airport and visit Paris.
In Schengen area a transit visa would only allow you to transit through the airport, and would not allow you to leave the airport and visit the city. To visit the city you'd need a short stay visa, which is basically a typical "tourist" visa. And while you're exempted from having a transit visa (which Indian passport holders are required to have) due to having a US visa, you'd need a short stay visa if you want to visit Paris.
However please note that CDG is quite far from the city of Paris, and it will take you at least an hour (likely more) to get to the city after you clear the passport control - and this can take another hour. Considering that you'd have the same train and passport control on your way back from Paris - plus airport security on top of it - and that you'd have to be at your gate no later than 40 minutes before the flight to US, you don't have much time to spend there.