Wikipedia is "crowdsourced" which is a hip way of saying that it's written by a lot of people who happen to be volunteers. Put another way, "Anyone can put anything they want on Wikipedia."
In a way, that's true. One of Wikipedia's five most important beliefs, know as the Five Pillars, is that "Wikipedia is free content that anyone can use, edit, and distribute." What's not mentioned is that Wikipedia has tens of thousands of editors who work diligently to make sure that content conforms to a well-thought-out set of policies and guidelines.
While anyone can post whatever they want, there's an army of volunteers who devote mountains of time and effort (some edit 40+ hours a week and make thousands of edits a week). That being said, those volunteers tend to put their focus into articles that have the biggest impact.
Put another way, the articles with the most views get the most attention from editors. An article about a little-known actor on a TV show that was cancelled after one year, shouldn't be expected to be as full and accurate as say an article on a person like Bill Gates or an actor like Tom Hanks.
When you ask "Can I trust what I find on Wikipedia?", the answer is that you should read every article (and everything, for that matter) with a healthy dose of skepticism. If you find a statement that you're questioning the validity of, check the reference associated with it (click the little number at the end of the statement, sentence, or paragraph and it will take you to the reference).
The next logical question is, "Can I trust this reference?" This is a big question which I'll cover in another post about what Wikipedia calls Reliable Sources.