REPORT and Dataset

Hi Experts,

I am new in Power BI , and I have some Basic and fundamental Questions :

1) Could I create Dataset  base on more than one table from DB?

2)Is there any place to define level for measure or define aggregate function different from function which is used in Measure ?

3) How could I define parent-child relation between column from different tables?

I really appreciate your help

Regards

Matin