If I remember correctly, the comparative advantage was first mentioned by Adam Smith. The competitive advance is one of the theories that Michael Porter developed.
The comparative advantage describes the situation where an individual, a company or a country is able to product specific goods at a lower cost compared to other companies, countries etc. The reasons for the existence of this advantage include access to information, highly trained human resources, access to natural resources, geographical location and others.
In simple words, the theory says that we should focus on things that we need know how to do better than other people (and at lower costs) because we can dominate the market due to the unique position we have.