English is fine and your questions are clear and understandable.
You do not say which Mac you have, so the exact ram configuration will depend on the Mac. Macs are very sensitive to their memory so buy your ram from a reputable Mac supplier and be sure the ram is certified for Macs, a lot of PC ram will not work with a Mac since it is not accurate enough in timing. Good sources are OWC and Crucial. You can go to either of those websites and see exactly what memory your Mac will accept.
They also have on-line videos that show how to do the installation.
If you want to upgrade from Snow Leopard to Mountain Lion, be sure your Mac is on the compatible list at http://www.apple.com/osx/specs and with your planned memory increase you sould do well.
BootCamp can probably be left as it is now if it is performing as you want it to.
Crucial have a nice guide where you choose which model mac you have and it show compatible models and speeds of mem
used to find the price of a 16GB upgrade which the fact that mem prices globally raised by 35% made me push the purchases of a bit