In Power Query, data cleaning and transformation involve several key steps to prepare raw data for analysis. Initially, you import data from various sources such as Excel, databases, or web pages. The cleaning process includes removing duplicates, filtering rows, and correcting errors. Transformation steps involve renaming columns, changing data types, and merging or splitting columns to structure the data properly.

Advanced transformations include unpivoting columns, creating calculated columns, and aggregating data. These actions help ensure the data is accurate, consistent, and ready for creating insightful visualizations and reports in Power BI.