OpenStreetMap (OSM) follows a similar concept as Wikipedia does, but for maps and other geographic facts (despite its name, it's by no means only limited to streets and roads). People, like you and me, gather location data across the globe from a variety of sources such as recordings from GPS devices, from free satellite imagery or simply from knowing an area very well, for example because they live there. This information then gets uploaded to OpenStreetMap's central database from where it can be further modified, corrected and enriched by anyone who notices missing facts or errors about the area.

Anyone can freely download and use the full information for any purpose they like under an open source license. Currently the most prominent use of OSM data is to render beautiful, rich maps such as the examples you can find on www.openstreetmap.org, but there are plentiful other applications too.

The project was started because most maps you think of as free actually have legal or technical restrictions on their use, holding back people from using them in creative, productive, or unexpected ways. To foster these creative and unexpected uses, OpenStreetMap also does not limit the type of information people can add into the database, as long as it is factually correct, verifiable and does not infringe on anyone else's copyright. You never know for what interesting purposes it can be used for in future...

This Beginner's Guide covers the process of adding data to OpenStreetMap. To get an overview of the site's features and the surrounding community, you may also want to watch a quick introductory video online to get you up to speed (one of several video tutorials)

To add data to OSM, you need to register a user name with OSM here. If you want to edit this documentation wiki, you can signup here; these are two separate logins.

The 5 steps to add to OpenStreetMap

Further documentation

More advanced questions, and FAQs can be found on their own pages around the wiki
Additional information is available here.
Additional help from the community can be found in various places.
If you are still a little concerned about beginning, read this article, OSM Mapping (using Potlatch) for Dummies [1]
How to get involved
Help on editing/updating the Wiki is available on the Wiki help page
A list of software that supports OSM data can be found on the OSM software page
If you want to add quick annotations to the map so a more experienced mapper can have a look at it you can use OpenStreetBugs.
To get some inspiration of all the things that can be mapped (well it is basically limitless...) have a look at some of the best mapped places

Additional Help

Help from other OSM members can be found in a range on places.

Forum - You can go to the forum for further help.
IRC - Ask in the OSM chatroom (IRC, Internet Relay Chat). Connect via the web or using an IRC program such as mIRC (Windows), Colloquy (Mac) or kvirc (Linux): then choose server irc.oftc.net, room #osm.
Mailing List - Get on the newbie mailing list or one of the other mailing lists. Specifically - get on the one from your country.
User Groups - Find an OSM User Group in your area.