President Obama addressed the people of Africa on 28 July 2015 at the African Union headquarters in Addis Ababa, Ethiopia. His speech, in my view, was the most important one he has ever made on the subject of Africa. You can listen to and watch the delivery here by going to the tab under 28 July 2015.
You can read the text of the remarks as delivered here.
The Institute for Strategic Studies published on 29 July 2015 a good analysis of the speech titled "Think Again: Why Obama's AU Speech Matters" by Simon Allison.
The Washington Post published on 28 July 2015 an analysis titled "Despite Economic Gains, Obama's Work in Africa Is Unfinished" by Juliet Eilperin and Kevin Sieff. It also comments on the speech at the African Union.