Python is the most famous language one for machine learning. If do you want to see how can R used for machine learning, you can have a look at this article. It will start with the basic statistics knowledge.
"Which is better tool for Data Science? Do I need to choose one of them or can I use both of them? Are both of them open-source tools?" If you are looking for information related to those questions and feel stuck to make a choice, let's look together deeply.