Can anyone explain to me why you change facts to mFacts? what does the m do?

That means.. "member variable" so we used "m" usually that helps with understanding scopes for example if you have a class called Bakery

public class Bakery {
  private String cookie;

  // Methods (abilities of the object)
  public void setProducts(String cookie) {
    cookie = cookie;
  }

it can be confusing to know which cookie you are assigning to which. The "cookie" on the right side has scope only inside the setProducts method (and is the variable passed in the method) while the "cookie" in the left side has scope inside the whole class called Bakery (and it's the one in " private String cookie"). So in order to avoid this confusion and differentiate things he added "m" which signifies member variable so that it will be easy to tell which variable you are using. So my example with a member variable changes to...

public class Bakery {
  // Member variables (properties about the object)
  private String mCookie;

  // Methods (abilities of the object)
  public void setProducts(String cookie) {
    mCookie = cookie;
  }

and now you can understand which variable is each and also clearly see its scope.

I hope this example helped.