The anti-reverse system is a switch on the reel that can be flipped on or off. When it is on the reel handle will not turn backwards. This ensures that you don't create slack line when you set the hook on a fish. A reels line capacity is a measure of the amount of line of a certain lbs. Usually, the larger the reel the greater the line capacity.
Ball bearings make the reel easier to operate by reducing friction on moving parts.
The more bearings a reel has the better. An average reel has about 3 ball bearings while the most expensive reels can have as many as 11 ball bearings. These types of features will generally increase your casting distance and make your reel smoother, so look into them. You should take your reel apart a couple times a year and clean it. Wash and dry off everything inside and outside of the reel taking care not to damage the bail spring.