Creating a new article is often a very useful thing to do, especially if there are lots of articles linking to an empty page.
Wikipedia articles contain lots of links to other articles. Blue (or purple, if you have already visited them) links represent pages that do exist. Red links point to pages that don't yet exist. Presumably, whoever created the link thought that an article on the topic should exist. It's possible this was a bad idea, and the link should be removed. It's also possible they made a spelling error or didn't know the correct name for a page on the same (or a more general topic) that does exist. In this case, you could fix the link, and/or create a redirect. If you decide there should be an article at the other end of the link, by all means start writing it!
In addition to looking for red links, you can look at a list of requested articles, and pick one you know something about. (See the section "Where do I start?" below.)
Even new users can help answer factual questions on the Psychology wiki:Reference desk, which serves the same purpose as a reference desk you might find in your local library. (You might also think of it as the the Psychology Wiki version of Google Answers.) You don't have to be an expert onthe Psychology Wiki because:
You can help people find answers in existing Psychology Wiki articles.
If you know the answer to a question not answered by the Psychology Wiki, you can assist the questioner and at the same time, add that information to the Psychology Wiki for the benefit of future readers.
If you don't know the answer to an interesting question, you can research it in non-Psychology Wiki sources, and then improve the Psychology Wiki for the benefit of the questioner and future readers.
Make a list of everything you know. Strike through the things that are not verifiable or not supposed to be covered by Wikipedia. Then, find the proper places to write about the items remaining on the list. Use the go button, the search, or just navigate by following links. Click the "What links here" link on pages you visit.
Things you might know about...
Things you have already done research on. Have you written a thesis, essay, or school paper? Consider contributing the fruits of your efforts to related Wikipedia articles. You probably don't want to dump the raw text of your essay into the wiki. First of all, there will almost certainly be an existing article which you will want to merge your content into. Secondly, Wikipedia is an encyclopedia. Articles that are not written in an encyclopedic style should be rewritten that way, or at least tagged Template:Tl:cleanup-tone. Also keep in mind that Wikipedia is not a place to post original research. This means that if you make a new discovery or come up with a new theory, you should find someplace else to post it. What we are about is researching and summarizing ideas and information that have already been publicized elsewhere. Most papers written up to the undergraduate level do exactly this. For technical help, see Wikipedia:How to import articles.
Current events. Wikipedia articles constantly need to be updated to reflect recent developments. Wikipedia also has an important role to serve in publishing background information that helps people understand current events and issues. If you hear a news story on your favorite news source (check out Google News if you don't have one), check Wikipedia's coverage on the topic! Remember that Wikipedia is an encyclopedia; if you want to write your own news stories, use Wikinews.
Do you know a foreign language? Add interlanguage links to articles! Translate an article or two! Or check out one of the many translation tasks listed under the "Start with a list of things that need doing" section, above.
Specific countries, provinces, counties, cities, and towns. Maybe one you've lived in, maybe one you like to visit. Start with the list of countries to find a place of interest. (But remember Wikipedia is not a travel guide; see Wikitravel for that.)
What are your favorite subjects in history, entertainment, or sports?
What are your favorite books (especially non-fiction)?
Do you know anything about your local political or religious leaders? Find them on one of the lists of office-holders.
Are you a fan of anyone who should have an encyclopedia article? Find them on one of the lists of people. Are they properly indexed according to birth and death date?
Feed your appetite for knowledge. Pick a subject about which you know relatively little but have always been curious or want to remedy a guilty ignorance. If you already know a lot about something, the best references in the field might know more, or might be a helpful reference for other readers or helpful to you in your writing.
Try to find good online and print resources, both books and journal articles. Using good references is a way of improving the credibility of Wikipedia, which will be increasingly important as Wikipedia grows and becomes more and more relevant. Then cite your sources. By citing sources you avoid copyright violations and plagiarism as long as you use only acceptable portions of other works. Doing research also makes it easier to think of material to add and allows you to improve any article, even one you didn't know much about.
Write about something you don't know about. Use this as an excuse to research a new topic. As you learn about it, write what you are learning here on Wikipedia. This is actually a good study aid because it forces you to take notes, to organize information, and to put what you've learned into your own words. You can take how to write a great article as a guide.