An assessment is a test of some sort. A survey is also composed of a set of questions. Unlike assessments, surveys are anonymous. Therefore, you cannot grade surveys or provide user feedback. You use surveys for polling purposes, instructor evaluations, and random checks of knowledge.
You build both tests and surveys by:
Creating questions of different types: Fill in the Blank, Matching, Multiple Answer, Multiple Choice, Ordering, Short Answer/Essay, or True/False questions