obviously a draft, but there's no such page and users seem to expect it.
To see what formats Browse supports, type about:plugins in its location field and press the enter key. (If you don't see its location field, click its "Browse" menu.)
The primary open unrestricted file format for audio and video files is [OGG]. So if you see a link to a .ogg file, your XO can probably play it. This is a "container" format for many different ways of compressing files. The standard OLPC system software can understand some but not all of these.
What happens with an unsupported codec in a .ogg file?? - need link
What about MP3 files?
Note that the standard OLPC software does not support common-but-restricted media file formats such as .mp3. See Restricted Formats for an explanation why.
However, it (should) be easy to add support for these, at the risk of violating software patents. See GStreamer#MP3.
Need a link to good sample files
Maybe Data file formats should have a link to a sample of each kind.
Other media players
There is a Jukebox audio/video player activity.
Besides running Totem as a browser plug-in, you can also start it from the Terminal Activity. You can install and run various other media players for Linux such as XMMS, see Category:Linux software. None of these are Sugar activities, so they do not interact with files in your Journal.
Wikipedia Commons has lots of files in .OGG format.
Also See Content repositories ??
Flash is an animation format that can also incorporate music and video.
The OLPC system software comes with the Gnash browser plug-in which has some support for Flash.