My 3D Cursor follows my selection cursor everywhere I click. How do I stop this? This happens to me every now and then in different projects and I never know what causes it. Anywhere I click, my 3D Cursor and Selection Cursor both move to that point and I cannot separate the two. How do I fix this?
You discovered the Pivot Point

This is a very useful feature in blender 

Your pivot point is for example the rotation axis. 

Maybe you want to rotate something around a Point then select a Vertice/Edge/Face/Object  press  Shift s to position the 3D Cursor.

Now press r and you will rotate aroud the 3D Cursor