The basic specification of binoculars is usually expressed in two numbers, e.g. 8 x 50. The first figure tells you the magnification. The second figure tells you the lens size. The reason that the second figure is important is that a larger lens will mean a brighter image.
Although many people buy binoculars which have very large magnification figures (e.g. 30x or 40x), this isn't always a good idea because, at these magnifications, it's very hard to point the binoculars in exactly the right direction to view your chosen object and even harder to keep the binoculars steady enough to view properly. For most purposes a magnification figure of 8 or 10 is probably ideal.
As with all optical devices, the quality of lenses can vary greatly between manufacturers. One of the main reasons that the professional wedding photographer gets better quality pictures than the wedding guest with a disposable camera is that the professional paid over �1000 for the lens on his camera. Quality lenses cost money and this applies to binoculars as much as cameras. (The lenses in most binoculars usually have a coating to reduce 'flare' in the picture you see. The quality of this coating also varies depending on the price you pay).
A final point. If you're looking for cheap, good quality binoculars, don't go to Argos. It's not that there's anything with their products -the Praktica brand, in particular, provides excellent value - it's just that you can't 'try before you buy'. The only way to see if a pair of binoculars suits your needs is to step outside the shop and try them out. You'd have to find a very quiet time at Argos if they were to be happy about you doing this. Instead head to your local Jessops store (where they expect customers to test their products before purchase). You can find your nearest store, and check out their prices, here:
http://www.