How to make a multi color map with one shapefile layer in QGIS?

I am working with a shapefile layer of the world. All the countries are in the Attribute table each one in a different row. I tried to make each polygon in a different color so the countries will be in a different color, but it did not work.

In the Africa map I save each polygon separately and upload into a new QGIS. This method takes a lot of time. What would a better and faster method be?

Answer

You may right-click on the layer in the Layers Panel and go to Properties >> Style dialog.

Then, choose Categorized, set the field that stores the name of the countries and click the Classify button:

Finally, click the Apply button for applying the changes and you will see this: