3 million per year for 4 years.

if the Jets cut him they still owe him the 3 million for the four years.

However, if another team signs him they get to reduce what they owe him each year by the amount he gets paid by the other team.

For example: if the other team signs him for 2 million per year, the Jets owe him one million per year.
if the other team signs him for 4 million the Jets owe him nothing.

So, in this case Zach gets to collect at least three buckets of shells (dollars) each year from the Jets or some other team.