Usage Policy Requirements

Can anyone please explain what does the below points in requirements in the Usage policy mean.

1. Provide a valid HTTP Referer or User-Agent identifying the application (stock User-Agents as set by http libraries will not do). => can someone give an example of this? Should i register User-Agent name somewhere?

2. Clearly display attribution as suitable for your medium.

3. Data is provided under the ODbL license which requires to share alike (although small extractions are likely to be covered by fair usage / fair dealing). => last two points are not clear to me.

I am currently reverse geocoding like below on my development site,

http://nominatim.openstreetmap.org/reverse?json_callback=cb&format=json&lat=40.119198&lon=-75.355764&zoom=27&osm_type=N&addressdetails=1

what should I add in addition?