It's a common phrase used to express that things are going well in your life, generally speaking. You could use it to describe:
* Your overall well-being: "I'm healthy, happy, and content"
* Your work or school: "I'm doing well in my studies/job"
* Your personal life: "I'm enjoying my relationships and hobbies"
It's a positive and upbeat phrase that can be used in a variety of situations.