Dragging Fact and Dimensions Tables
To create your cube schema you need to drag a Fact Table (Measures - values you can operate with) and Dimensions Tables and drop them to the workspace, preferably putting the Fact Table on center and the Dimensions Tables surrounding it, for better comprehension.
When you already have your cube structure complete, you can proceed to the next step.
Selecting fields from Fact and Dimensions tables
To select the fields to analyse just click on the respective checkboxes. You will note that the checkbox change its state, indicating the field was chosen. In addition, you can see a tree on the first panel (left side of the window), representing your SQL query with selected fields in it.
Making Joins between tables
To make a join between two tables, select a field drag it and drop it into another field of another table, it will appear a dotted line showing the join. In this step, you must be sure that the join you made is properly done.
This procedure also will be represented in the left's panel, where you will be able to delete any join you made by doing right click and selecting "Delete Join" option over the element you want to remove.