Well, it was South America first, by the Spanish and Portuguese.

These two nations saw a golden age, the Portuguese during the 16th century, and the Spanish during the 17th century respectively. They were the first to really be able to safely, or albeit more safely across the Atlantic and have access to royal support for this exploration. The time of Spanish exploration coincides with the time of Isabella and Ferdinand forming a united Spain after successfully kicking out the Moors from the Iberian peninsula. Upon arrival they wanted to essentially profit from the resources in Southern America. The main resource being gold, in fact, the discovery of this gold helped grow the golden age of both nations, until the availability of gold decreased which correlated with a decline in Spanish and Portuguese colonial power.

After the Treaty of Tordesillas (Spanish and Portuguese agreement to spilt the world in two amongst them, Spanish got the West hemisphere, the Portuguese got the East hemisphere), Portuguese existence in the western hemisphere saw a decline as they looked to explore elsewhere, we see this with Bartholomew Diaz, the first person to successfully navigate the WHOLE way around Africa as opposed to travelling to India via Southern America, and the first to arrive at the Cape of Good Hope (Cape Town, South Africa) in 1488.

The Spanish subsequently left to their own devices in the Southern Americas, they attempted to convert the local population, and notably by severe force as many noted including Bartolomé de las Casas, a Spanish historian who documented colonial atrocities of the indigenous populations of South America in his book Historia de Las Indias.

In regards to your question, why did Europeans see themselves as superior, they saw the lack of religious belief in God by the local populations as a sign of weakness amongst other things. The lack of agricultural 'know-how' and technology also spurred European-superiority beliefs that still existed centuries later in the eventual colonisation of the American colonies by the British and French.

Feel free to ask more questions, I didn't want to answer your question about the Columbian Exchange however, as I feel I have forgot some major aspects to it, hopefully someone else can answer it for you!