Power BI is a business analytics service provided by Microsoft. It provides interactive visualizations with self-service business intelligence capabilities, where end users can create reports and dashboards by themselves, without having to depend on information technology staff or database administrators

1.SQL Server/ MSBI /Power BI Online Training

2.Power BI Introduction Tutorial For Beginners | Power BI tutorial

3.Live connection / Direct Query and Import in Power BI | Power BI tutorial

Power BI – Live connection vs. Import, comparison and limitations
import it is mainly refresh frequency, data size and necessity to duplicate same logic (calculations, security) in multiple reports. That could be helped by templates, but if you need to change logic of calculation, you need to change it in multiple reports again. For live connection, not all data sources are supported. If you pick one, then you’re limited just to that one data source for report. If logic is setup on source side, all reports can benefit. My personal preference is use live connection against SSAS models, have the model centralized and maintain logic in one place. For SQL Databases where I don’t have model, I prefer import and use Power BI as a model and vizualization