First off - the last sentence isn't needed
We're here to help you with your problem, not tell you how amazing you are
Any currently open programs, games, etc, are held in the RAM while they are open. If there isn't enough RAM for them all to be put in the RAM, then they are put onto a space on the hard drive, which is much slower. Therefore, you want to have enough RAM for all your programs to be in the RAM.
Depending on your specs, adding an extra GB should be fine. However, if your motherboard can support Dual Channel RAM, then it would be better to add another 3 sticks of 512MB, preferably in a way so that you have 4 identical sticks of RAM, with the same timings and speeds made by the same manufacturer.
Any other questions, just ask.