Power BI is the business intelligence tool launched by Microsoft, It can be used to handle the data from different sources and use that data for visualization once data cleaning and integration is done. Interactive reports can be created in Power BI desktop then one can publish those reports in to Power BI services (like cloud). In Power BI services dashboards can be created and one can share those dashboards with others through power bi services. It’s very easy tool that can be used by naïve users as well as experienced users also.
To understand the difference between Tableau and Power-BI, you can read Tableau vs Power BI.
On the other hand Tableau is also a business intelligence tool that can be used to create interactive charts (worksheets), Dashboards and stories so that one can easily draw the insights from the visualizations. Tableau has the capacity to handle the huge data set but power bi can’t. In tableau you can import the data set from multiple data sources as compare to Power BI. It also helpful for the users to understand the data without need of any technical knowledge with very simple and efficient approach.
To learn tableau from basic to advance level check tableau certification