Getting started with the web is exactly the same as getting started with any research.

You want the correct tools and the correct search.

We will talk about choosing tools in the next tab, but you will likely be picking a search engine (e.g. Google).

For a good search (just like using the catalog or the Library's databases), you want to choose key concepts -- terms that are necessary for your topic and as concrete as possible. Your research question is a great place to get key concepts. Leave out words like "a," "an," "of," "in," and so on. They won't do you any good and they will mess you up.

So, if your research question is "What are effective treatments for teenagers suffering from depression?" your key concepts will be "treatments," "teenagers," and "depression." Words like "what," "are," "for," "from," and even "suffering" are unnecessary -- they will just gum up your search (yes, suffering -- no one enjoys being depressed, so why include it in your search?). "Effective" is also unnecessary, since you will have to read and understand the sources you find to determine which treatments are effective.

You can also include synonyms -- words that mean the same thing. In the example above "teenagers" could also be "teens" or even "high school students," depending on how you define "teenager" for your research.

If you are looking for pro and con arguments for a social topics paper, "pro" and "con" are too vague to be keywords (especially since they could be short for "professional" and "convict"). You are better off getting an idea of how the various sides of the issue talk -- for example "physician assisted suicide," "euthanasia," and "right-to-die" are used by different groups interested in that social issue, and using one term over another will tend to get you sources that focus on that side of the debate.