Hi Marion,
I usually just search in the search box of wiki.openstreetmap.org when I don't
know a tag.
doctors leads to : amenity=doctors
Dental to : amenity=dentist
Optometrists to : shop=optician
...
browsing the map_features page can also give ideas
Hi Marion
I'm no expert either, but generally the OSM wiki is a good place to start:
http://wiki.openstreetmap.org/wiki/Tag:amenity%3Dhospital
It gives useful guidelines like Hospital is bigger than Clinic. Clinic is
bigger than Doctor, and it also answers your query about emergency