A screencast that walks through how to upload files to Wikimedia Commons and add them to Wikipedia articles.
Images, audio and video files must be uploaded into Wikipedia using the "Upload file" link on the left-hand navigation bar. Only logged in users can upload files. Once a file is uploaded, other pages can include or link to the file. Uploaded files are given the "File:" prefix by the system, and each one has an image description page. Please consider uploading freely licensed content to the Wikimedia Commons instead of here. This allows the files to be used in articles instantly by all Wikimedia projects. Files from Wikimedia Commons use the same syntax described below, there is no extra step needed. The maximum size of an uploaded file is 100 megabytes. As of March 2012, the following file types may be uploaded: png, gif, jpg/jpeg, xcf, pdf, mid, ogg/ogv/oga, svg, djvu. All others are prohibited for security reasons, and pdf and djvu are intended primarily for projects like Wikisource.
If you want to give a link to the file description page in an article, use an extra colon at the front, e.g., "[[:File:pagename". If you type "[[Media:pagename]]", a download link to the media file is created. The page name will contain the file type such as pagename.jpg.
It is not necessary to upload images to use special characters or even complex mathematical expressions.
Wikipedia uses a UTF-8 encoding scheme, which means that any Unicode character can and should be entered directly. See m:Help:Special characters for details and help. (You can also use SGML entities for certain characters, such as & for & or é for é.)
For mathematical formulae, we use TeX markup. For help and instructions, see m:Help:Formula.