There are three levels of college degrees. From lowest to highest... Undergraduate degrees, graduate degrees and terminal degrees.

Imagine that college is like regular school you are already familiar with undergraduate degrees are those you earn in "four years or less," Graduate degrees are an additional 2 years post undergraduate and terminal degrees are the highest level of degree that one can earn in a field (if you ignore law and medical school,) these are typically 4 years (or more) after your undergraduate degree and entitle the person to call themselves doctor.

The term doctor can be confusing as it didn't originally have anything to do with medicine as is commonly believed today.