Make an edit with JOSM
Install the JOSM editor, if you haven't already, and edit something with it. We recommend drawing some buildings:
Download a part of the map, add an imagery layer, press "A" and click on a corner of a building. Then double-click on an adjacent corner, making it a line. Then press "X" and drag the line out to make it a rectangle. Finally, press "Alt+A" to add building=yes, and then upload the change.
To track your progress and get more advanced tasks, sign in with your OpenStreetMap account.