On Wikipedia, much of our editing is an honor system. This means that editors are trusted to obey all the rules and do the right thing. There is no central authority and no police force, just the assumption of good faith.
How Wikipedia is an honor system
Addition of information
When any article is created or information is added to an article, it is assumed that the editor is acting in good faith and that all the information is true and correct. But there are some safeguards in place. References are required for all information, and new pages are patrolled to determine whether or not they belong. Unverifiable information can be challenged and removed.
Use of references
It has been a long accepted standard that all information included in articles must be verified with reliable sources. Despite this, quite a lot of information finds its way into articles lacking this. Much of it has been added in good faith by those unaware of Wikipedia's citation policy, or else who are aware of it, but they know that what they are adding is true and correct, and either they do not know where to find any sources, or they do not feel like making the effort.
Many sources can be found online. But offline sources are equally valid to establish notability and verify information. Offline sources can be difficult for most people to find and trace, since they are often found only in certain libraries, archives, or in other places where access is limited to a small number of people. Therefore, editors are trusted to be truthful about these sources.
Wikipedia has a one editor-one account policy for most situations. With some exceptions, each human being who edits Wikipedia is expected to have only one account and to use this account to make all edits. Having additional accounts in violation of these guidelines in order to pretend to be more than one person, stir up controversy, cast multiple votes, or to hide certain edits is known as sock puppetry. Of course, it is not always easy or possible to determine who is violating this policy. While a checkuser inquiry is sometimes performed and other signs are monitored, at best, users are expected to be honest in this regard.