Understanding Wikipedia’s core content policies is essential to becoming a successful contributor. Today, a brief introduction to the three considered most important:
Neutral point of view (NPOV): This is probably the best-known rule of all: Wikipedia articles are not supposed to take sides. In both content and tone, Wikipedia should fairly represent all relevant views.
No original research (NOR): Wikipedia is not a place for you to write things you happen to know. Rather, it’s a place to write things that others have previously published.
Verifiability (VERIFY): Cite everything. Editors don’t always include citations for material they add, but in theory, any information included must be attributable to existing sources.
To be sure, all three rules are broken on a daily basis. Determining what "neutral" means, or what a source truly says vs. what it might just imply, can be a challenge. Which is precisely why Wikipedia needs editors.