If you're new to mapping we recommend watching the videos in the 'Beginners' section to get up and running. If you've mapped before follow the 'Map Now' link, or consider learning to validate. There is also additional tutorials available via LearnOSM.
Go to the OpenStreetMap website and register to create an account. Follow the link in the email they send to confirm your account.
Go to the Task Manager to find a project and task that interests you. Learn how to lock a task to edit, select an editing program and change the background settings.
Buildings are one of the most useful things you can add to OpenStreetMap (and they're fun too)! Learn how to add and edit buildings to OSM through the iD editor.
Roads are also one of the most useful things you can add to OpenStreetMap! Learn how to add and edit roads to OSM through the iD editor.