Learning Power BI is a really good decision as managing big data is much needed right now.
Microsoft Power BI's official page has pretty good documentation, you can just learn from there. Moreover Edureka has a few blogs and videos on Power BI with good hands on demos which will be helpful.
Have a look at these links:
This is the entire playlist and it starts of with very basics of Power BI so should be pretty clear.
Also Edureka provides certified courses as well which has been very helpful for a lot of people.
Happy learning :)