Adding a Condition 
You can add more conditions after you have created a Decision Table. Conditions in a decision table represent the If section in an If-Then Rule.
Locate the ruleset (Where is my ruleset?) and double-click the ruleset node.
In the Outline view, choose a decision table node.
In the decision table editor, choose the Condition button.
In the menu that appears, choose either Add Vertical Condition or Add Horizontal Condition depending on how you want the layout of the decision table to appear.
More Information: Changing the Layout of the Decision Table
If you choose Add Vertical Condition, press Ctrl in the dialog box that appears and choose the aliases to be included as conditions in the decision table and choose OK.
If you choose Add Horizontal Condition, choose an alias in the dialog box that appears and choose OK.
Note
If you have already added a horizontal condition in the decision table, the Add Horizontal Condition option is not active when you choose the Condition tab in the decision table editor.
Save the changes.