Could you please explain how you expect our defense to improve with the staff and player moves over the off season [Like I'm 5]

I consider myself to have a fair/average amount of base football knowledge, although I didn't really start enjoying football until college (Geaux Tigers.) and I did not grow up with it or play it. I love football, pro and college, I'm a fantasy football fantatic. But with all that, I've never really understood basic defense schemes, or what our biggest problems were last year. I knew Spag was bad before he made it to the Saints because of his last season with the Rams. But why?

Any in depth explanation is appreciated.

TLDR:

- What was the issue last year?

- What are we going to do differently?

- Who do you expect to make the difference?