I did a search but couldn't find what I was looking for (I will admit to running out of patience!

).
I am getting ready to order a band but I want to make sure I am ordering the right size.
This is the one I am getting. I am guessing I should start with the strong band, right?
I can't do any pullups and I am quite over weight. If I understand correctly, the "resistance weight" listed on the band will, essentially, subtract that number of pounds from my body weight during the pull-up. Is that right??