There are many online websites who teaches Data Science for free but there are very few who provide quality training.
For learning Data Science, first of all, you need to learn Python or R programming.
Then you need to move on to Data Mining, Data Visualization, and Machine Learning techniques and algorithms.
Also, Data Science has a very bright future ahead and if you are a beginner who eagerly wants to learn Data Science then go through this comprehensive Data Science tutorial.
Also, if you want to learn Data Science comprehensively then you must watch this video tutorial on Data Science:
Last thing, Certification acts as a hallmark for your skills, so, you must go for Data Scientist because it is a Live Instructor-Led training with real-time industry-oriented project.