It uses as much memory as it needs for the given task. You really want it to use as little memory as possible.
Actually there is an option (setting) as to how ram is allocated to Adobe applications.
Check the Preferences (I cant remember where it is)
Edit -> Preferences -> Memory
Then you'll see a certain amount of memory allocated to Adobe applications and "RAM reserved for other applications" which you can tailor to your own computer. If you ONLY want to do video editing then you can crank down the amount allocated to other programs.Take care though, if you run anything else you might end up swapping memory to disk and slowing things down.
Of course, you can monitor this independently in Task Manager on Windows (not sure on Apple) and keep an eye out.