Cube creation in SSAS

Hi Experts,

I am following through the examples in MSDN on the creation of cube using SSAS.

Basically the steps are clear as following:

1) Create new SSAS project

2) Create new data source

3) Define new data source view

4) Define dimension and measures

5) Deploy the cube

In step 3 ie Define Data Source View, it mentioned to select the DimCustomer, DimDate, DimGeography, DimProduct and FactInternetSales tables.

The when defining dimension, the tutorial mentioned to select certain set of attributes

My question is, why are those tables selected as the Data Source View and why those attributes selected when defining the dimension?

Thanks