You buy the base coach madden for 10 trophies and put him in your lineup. He will appear on your sideline as your coach... but he does nothing at this point to boost the stats of your players. To get boosts you need to buy "madden collectibles" for 1000 trophies each. You then "Upgrade" coach madden and pick one of the categories to boost... Run or Pass Offense... Run or Pass Defense... with your 5th one you get a "physical" boost that increases your Speed.
The boosts apply to every player in your lineup... so it's worth it... (but expensive).