star schema designing

Hi ,
Iam new one to datawarehousing.How to design the star schema.
we have the hr module(OLTP) which has 77 tables.
I have some basic doubts please anyone clear that.

http://en.wikipedia.org/wiki/Star_schema

For ex.
I followed the above link.

Whether OLTP table and dimension table are same or not.
If not,can we create the dimension tables from OLTP tables?

Fact_sales table has date_id,stroe_id,product_id and units_sold.

date_id refers dim_date.
store_id refers dim_Store.
product_id refers dim_product.
but units_sold refers what?


It is a big confusion to me?please anyone help me out that?

Whether OLTP table and dimension table are same or not.

No

If not,can we create the dimension tables from OLTP tables?

Yes

The basic thing to understand about dimensional modeling is the model is divided into facts and measures. Facts represent measurable business events or states and dimensions represent the context for the facts.