I can not adise you on computer security, but the resolution question is easy answered.
Your monitor can display graphics at different resolutions,800 by 600, 1024 by 860, the number refers to the number of pixels on the screen, the higher the number the better the resolution.
I have a 19inch diamond pro and I have the screen resolution set to 800/600 which is a good enough resolution for surfing the web ect.
Some programs such as flight sims will switch your monitor to higher resolutions for better graphic clarity.