So, how can you add to a Wikipedia page?
Adding information to an existing Wikipedia page is easier than creating a new page. However, it still requires some understanding of how Wikipedia works.
Fixing a grammar or style issue. This is perhaps the easiest edit you can make. First, make sure the Wikipedia page in question is really in error, not you. Then press the edit button and use the Visual Editor to fix it. Note, however, that some pages (especially contentious ones) will not be open for edits to new visitors. In those cases, you’ll see a “View Source” button rather than an “Edit” button. Here, you can explain the edit you want, and some other editor will do it for you. Alternatively, fully register in Wikipedia and prove yourself worthy to the community of Wikipedia writers. Then you’ll be able to make your own edits.
Adding missing information. This is more complicated because you will need to back up the fact that you’re adding information from a credible source. Ideally, you need to reference this source in the same citation style already used on the page. (Interestingly, Wikipedia does not have a unified citation style, but requires that within the same page, all citations follow the same style.) If this sounds too complicated for your first edit, you may want to do the minimum: add your reference in between two ref tags: <ref> </ref>. If your source is credible, another Wikipedia editor will take care of the formatting for you. However, if you try to cite somebody’s blog, a Facebook page, or a private YouTube video, your contribution will be deleted anyway, as your source has to be more credible. A credible source doesn’t have to be an academic journal, but it needs to be at least an established website with reasonable practices of editing and fact-checking, not self-published material.
Fixing an error on the page about yourself or your organization. Based on Wikipedia’s conflict-of-interest policy, don’t try to correct the error yourself. Instead, provide reliable sources that show how the page is in error, and suggest the proper change on the talk page associated with the article.