Last week, we covered "No original research", which tells you what not to do, i.e. add information you can't prove. The flip side is "Verifiability", which outlines what you should do: include links to reliable sources to verify that what you say is true. Well, sort of.
One of the more controversial notions on Wikipedia is that the threshold for inclusion is "Verifiability, not truth". Ideally, Wikipedia contains only facts that are true. But truth alone isn't good enough. Unless you can point to a respected publisher of information that vouches for the veracity of a claim, you can't include it.
And truly, verifiability isn't enough, either. It is a necessary condition for inclusion, but not alone a sufficient one. To make that call, we have to look at the sources—which we'll do next week.