Potlatch is the classic OpenStreetMap editor, combining an efficient user interface with attractive presentation and a number of powerful features.
Until 2020, Potlatch was available on the Edit tab of openstreetmap.org. Now that the lifetime of Flash Player has come to an end, Potlatch (version 3) is now available as a downloadable app for Mac and Windows.
To navigate to the place you want to edit, you can either:
Use the search button;
Zoom in with the zoom controls (shift-drag to zoom to a rectangle); or
Find the place you want to edit using openstreetmap.org on your web browser,
then click the "Edit" triangle and choose "Edit with Remote Control".
Once you've zoomed in sufficiently, the editable map will appear.
Click Help for a short guide to editing.
After making your changes, click Save. If this is your first time, you'll be asked to log into OpenStreetMap.
Enter your username and password in the pop-up window. This'll be saved for next time.
More detailed help is available within Potlatch and on this page.
Conversion of Potlatch to a desktop application has been generously supported by the OpenStreetMap Foundation. Thank you!
What's different in Potlatch 3?
Faster rendering
OAuth login workflow for saving
"Edit with Remote Control" support
Overview zoom levels
Use custom OSM-compatible servers
Overpass API support for Tasks palette
Are you a Linux user?
I'd like to make Potlatch available for Linux, but Adobe withdrew Linux support for AIR (the technology Potlatch is based on) a few years ago. If you're of a technical bent, older versions of AIR are available; there are some pointers on the downloads page.