Power Query is a powerful tool in Excel that allows you to gather, clean, and transform data from various sources, such as databases, websites, and spreadsheets. To use Power Query, you can start by clicking on the 'Data' tab in Excel and selecting 'Get Data' and then 'From Other Sources.' From there, you can choose the specific source you want to import data from. Once you have imported the data, you can use the power query editor to apply transformations, such as filtering rows, merging tables, or even unpivoting data. Power Query also allows you to create custom columns based on formulas and conditions. Finally, you can load the transformed data back into Excel and refresh it whenever your source data changes.