There are three groups of resources in this tab:
Sources (tables and views) listed in Database section come from the currently selected (default) schema. The Set button can be used to change the default schema:

+ Plus == Equal - Minus != Not equal X Multiply AND Logical AND / Divide OR Logical OR = Assign value of [ Start of variable name > Greater than ] End of variable name >= Greater or equal ( Start of group < Less than ) End of group <= Less or equal ; End of statement