Power BI is a suite of self-service business intelligence (the BI in the name) tools developed and maintained by Microsoft. The easiest way to understand self-service BI is to think of it is as DIY Business Intelligence. Power BI offers end-users a simple, yet powerful, interface for data modeling & data transformation, creating data-driven reports, and building visual dashboards.
Power BI Desktop is a freely downloadable version of Power BI that business analysts familiar with Excel love to work with. To share the Power BI Desktop created reports, you can use Power BI Service (Cloud/SaaS offering) or Power BI Report Server (on-premises server).
Data Modeling can be done in Power BI to shape data from various data sources. Power BI includes Power Query editor that lets you create queries to bring in data from various data sources, remove columns, reorder columns, append queries, and merge queries. Power BI also lets you utilize DAX expressions to create calculated columns. You can also create relationships between tables. You can also create reusable data models by using SSAS. SSAS offers two different styles of models: (1) Multidimensional databases/cubes (2) Tabular Data Model.