Turn on GPS on your Android device.
Launch the app.
In the upper part of the screen the actual GPS status is being displayed. Wait till signal is strong enough and you see your current position being displayed.
Now walk around.
You will see simple screen with numeric keyboard. This is used to enter house number of your current position.
If you want to add a number, use the dial pad to enter it. Press "Nxt" to save this position. A waypoint will be save to your active GPX track.
If you want to close the session, close the app. A status message (toast text) will tell you, if the GPX track was saved successfully to your SD card. A directory "gpslogger" will be created automatically and the GPX track will get actual timestamp as filename. Connect your phone via USB and download the track.
You can now use your OSM tool (e.g. JOSM) to edit OSM data.