You're not a rocket scientist. You're not even a scientist. Everything you need to know is right on this page. Typically, you pay more for one that weighs less, though it may not come with all the built-in features. The processor is the laptop's engine.
More megahertz means faster programs with fewer crashes or freezes.
Figure that 650MHz is relatively fast and 400MHz is a good mid-level. Don't get less than 200MHz. RAM is your laptop's short-term memory. Web browsers tend to hog it. The more megabytes, the better.