Ssrs 2010 shared dataset

In an existing ssrs 2010 report there is a shared dataset that I would like to know how it works. Here are are my questions:

  1. In the report there is a shared dataset called test. The sql that is contained within this dataset is appears to have the sql
    that is used within the report. When I compare the shared dataset called test that is contained on the right side of visual studio ide, the other datasets that are contained on the left side of the visual studio ide, what are the datasets on different sides of the visual studio 2010 ide? Is there a way to place the datasets all on the left side of the ide?
  2. What is the benefit of using a shared dataset? Can other reports access the shared dataset and if so how?
  3. This report uses a lookup ssrs call with the shared dataset. Can you tell me what this accomplishes?
  4. When using the visual studio management studio, it seems that the shared data is setup in a specific database. Is this possible? If so, can you show me/tell me how to access the shared dataset in the specific database?