What does mean the first sentence in bold and the second quote?
“You alone are enough. You have nothing to prove to anybody.” (Maya Angelou)
“Do the best you can until you know better. Then when you know better, do better.” (Maya Angelou)
The first quote is saying that each person has inherent value. You do not need to accomplish something incredible or prove that you are more clever than another person before you will be a worthwhile human being.
The second quote means to work to the best of your abilities. It is saying that the best of your abilities may not be the perfect way to do something, but if you keep trying, you will learn from your mistakes, and you will be able to do it better.
For example: The first time you ride a bicycle, you will not ride it well. You will fall off and you will scrape your knees. You did the best job that you could to ride the bicycle, but you still fell off. However, as you keep trying to ride a bicycle, you will improve and learn from your mistakes. If you keep doing your best for long enough, you will learn how to ride the bicycle properly, and when you do the best that you can to ride a bicycle, you will no longer fall.
I would like to give some context on Maya Angelou. She was a black civil rights activist in the United States during a period of desegregation. As a black woman in America in this time period, people regularly judged her based on the color of her skin, and decided that she was a less worthwhile human being than a white person. The first quote is saying that being a black woman does not mean that she can be judged as less than a white man.