How can i create singleton instance of an dependency class

I am bit new to patterns and using them. So please pardon my dumb question.

I want to configure an object of a dependency class(say A.) once and use it through out my app. I tried making a singleton wrapper class on top of it, but failed miserably. I tried something like:

 public class B {
  public static A a = new A();
  public static A getInstance() {
      return a;
  }

  private B() {
    a.configure(); 
  }
 }

I think calling B.getInstance() wont configure the object here. What i want here is to configure A's instance once and use it everywhere.

Would really appreciate help here. Thanks in advance.