Create Instance Using Reflection - How these methods are different?

While working on C# Reflections, I came across these methods:
1. Activator.CreateInstanceFrom()
2. AppDomain.CreateInstanceAndUnwrap()

My questions are:
1. What does Wrap & Unwrap means?
2. How does the two methods differs?
3. The 1st method forces the user to Unwrap the object. Why?