I have recently bought a Canon EOS 600D and I want to buy a UV filter to give extra protection to my EF-S 18-55 IS II.
And I additionally want to buy a lens hood as well.
Will I be able to use both at same time?
Yes, the filter has the same diameter as the lens so it won't prevent you from mounting the lens hood.
The other answers are correct: for this lens, the hood attaches to a bayonet on the outside of the lens, and the filter threads are still clear so that screw-in filters can still be added.
It should be noted, however that this isn't universally true: screw-in hoods are available, and for some lenses this is/was the OEM solution. Also, some filter options -- such as the large square filters from Cokin and Lee are pretty much always going to mean that there's no way for a hood to fit when using these systems. And lastly, if you've got a 77mm filter that you want to put on a lens with a 52mm thread you can use step-down rings to do so -- however I bet the hood won't fit over the large filter.
Yes. The hood doesn't attach to the filter mount. It attaches to an exterior ring.
You could attach a stack of 20 filters one on the top of another and the hood will still fit. (Of course you probably shouldn't use 20 filters at once!)