Official Docs: GlideQueryCondition

The scoped QueryCondition API provides additional AND or OR conditions that can be added to the current condition, allowing you to build complex queries such as: category='hardware' OR category='software' AND priority='2' AND priority='1'

addOrCondition

Adds an OR condition to the current condition. oper is an optional parameter

addCondition

Adds an AND condition to the current condition. oper is an optional parameter