Not certain which maps offering this question is about, since There are no HERE maps API offering for the Windows Phone 7 as such, the maps API there were using Bing Maps instead.
Anyways, if this is HERE Maps question, then the SDK API does not offer any Functionality for what you are asking, however there is Places API with HERE, which could give you the places and you could search those places by category.
For adding places, I suppose that currently the API does not offer any interface which could be used by normal 3rd party developer.