OpenStreetMap is a database of mapping information which can be used for many different purposes with very few restrictions (see copyright for more details in relation to usage and copyright). You can benefit from OpenStreetMap using the main OpenStreetMap page or one of the many many other information services based on OpenStreetMap available from many different organisations.
Newcomers should note that much of the value of OpenStreetMap is in these various very different services - and should remember that different services display different information and that they do so on maps in very different ways. Lots of information is available through these services which isn't through the main map page. Note the button at the top right of the main map which gives access to a very small selection of different map formats from such services.
The entire database is available for download from Planet.osm. This, however, is a very large file indeed and it may be more appropriate to download only the data relating to an individual countries and region using 3rd party information services detailed in the linked article.
If you notice an error or omission in the data/map then remember that changes or additions to the map information can be made using a simple editor.
This page provides some initial ideas and links to more information about uses of OpenStreetMap.
License and safety disclaimer
You can use OpenStreetMap mapping and data without charge subject to two conditions; firstly that you attribute your use of OpenStreetMap appropriately and secondly that you share any corrections or improvements back with the project as appropriate. See here: Copyright
OpenStreetMap is not a complete or accurate map of the world and should not be used in such a manner that deficiencies, omissions, inaccuracies or errors could result in death, loss or injury. See here: Disclaimer.
There are numerous services which display online slippy maps based on OpenStreetMap ('OSM') data. The OSM Online Browsing page highlights some of these, as does the OSM based services - and a few are available through a button at the top right of the main openstreetmap.org page. It is possible to create Static map images (rather than 'slippy' maps) for particular areas.
If you want to make a print or final image of the map there are various services which can create OSM on Paper. As with online mapping websites remember that what a printed map looks like isn't fixed.
Online and offline routing, GPS units etc
It can be useful to have the OpenStreetMap data for an area in your GPS. See the OSM on GPS article for details of how to do this. The Software article has details of many packages of software which you may want to use - but very simple solutions are often available too.
Main article: Downloading data It is possible to download portions of OpenStreetMap data (in .osm) that be can exported to a wide variety of formats (including SHP, POSTGIS, geojson) for many purposes, including use in professional GIS software systems.