You should be able to reach the Caribbean and/or Nova Scotia, by 1492, and once you set up permanent colonies, you’ll be able to expand further into the continent. Certain Idea groups, such as Expansion and Exploration make up for this over time, and extend your range. Depending on your Colonization Range, you’ll only be able to explore certain areas before you cannot reach the Terra Incognita that is too far out of range. If you have the El Dorado DLC enabled, the Explorer will explore the whole region, and return to the closest port for reassignment when finished. Send your Explorer out to the first sea province you can. If you’re starting at a 1444 start date, you’ll have to wait until 1492, because that is when the you’ll have enough monarch power to hire an Explorer. Colonists are vital to Colonization, because they set up the colony. The first Idea of Exploration Ideas adds a Colonist.

First make sure you’ve taken Exploration Ideas. Colonization is easy, and the best way to expand and gain wealth outside of Europe. Colonization is a pretty important part of playing a major Western European power (Spain, Portugal, England, France).