Why is it constantly hot in African countries?

Not entirely correct. Some of the Northernmost and Southernmost has what would be considered a Mediterranean climate. It is warmer in the Continent because equator runs through the middle of Africa, 

Because they are near the equatir which is near the sun

Most of Africa is between the Tropic of Cancer and the Tropic of Capricorn, which are 25 degrees North and South, respectively, of the Equator, this area is called the Tropics, and is is a band of of warmth around the globe because the Equator is where the sun shines for the longest period of the day every day of the year as it is the area of the earth that is always most directly pointed at the sun