I don't know how much you know about the numbers quoted with binoculars; apologies if I'm talking down to you. The first number is the magnification and the second number is the diameter of the front lens. The exit pupil is defined as the second number/first number eg for 10x50 binoculars the exit pupil is 5. This tells you how good the binoculars will be in bad light and 5 is the biggest useful number and good for star-gazing. For normal daylight use almost any value will do, so 8x25 would be perfectly good for daylight bird watching. At magnifications greater than 8 they become more difficult to hold steady, hence the advice to try some in a shop.