I have to travel to France and the transit will be on Dubai T3. Is it difficult to find gates and next flight there?
Three hours is plenty of time to transit Dubai airport. You will be fine. The only hold-up is usually when you disembark from the plane and go through security to enter the Terminal proper. However this is very fast and orderly.
When disembarking the plane, follow the signs for connections. Then go through Security into the Terminal building. Follow the signs to T3. Depending on your arrival Terminal this will include a short train ride. There aren't (IME) that many staff to direct you, but it's pretty obvious.
The main problems in Dubai airport are :
I do not have experience with this specific airport, but 3 hours of transfer time are in general enough. If you have any concerns, there are a few things you can do to feel more comfortable
Probably you will have two hours to relax after you found the gate. Try to find some nice meal, the restaurants are all indicated on the map.