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EdX Analyzing and Visualizing Data with Power BI - Free
Concepts and documentation - https://powerbi.microsoft.com/en-us/documentation/powerbi-service-basic-concepts/
Guided learning - https://powerbi.microsoft.com/en-us/guided-learning/powerbi-learning-0-0-what-is-power-bi/
Youtube video - https://www.youtube.com/watch?v=nOaeJ9D_9D4 (there are several more available online for specific topics within powerbi)