Power BI is a collection of software services, apps, and connectors working together. It helps to connect different data sources and get visually immersive and interactive insights from the data. Power BI creates powerful reports to be shared with others, as required. Data may be connected from different sources including files, databases, Azure services, Power Platform, etc.
If you need an introduction to Power BI, read Analyze Azure Cosmos DB data using Synapse Link and Power BI – SQLServerCentral. This has general information and a detailed case study on one of the components, named Power BI Desktop.