Green Card? Employment Visa? Temporary? Permanent?
I thought I knew what I knew.  After all, I have extensive personal experience with several "Green Cards".   
I was extremely surprised: I knew virtually nothing.
Jason Finkelman opened my eyes.  Immigration to the United States is complex.  It can be very expensive, too, especially if you don't know what you are doing. 
Regardless of your reasons, resources, or knowledge, your first step should always be to speak with an Immigration Attorney.

Helpful links:
start here: the United States Citizenship and Immigration Services https://www.uscis.gov/
For some statistics,  click here: https://fas.org/sgp/crs/homesec/R45938.pdf
To speak with Jason Finkelman, click here: https://www.finkelmanlaw.com/