You'll get a fixed payout from your defined benefit plan. That payout can be either a lump sum or a monthly check - you usually get to choose.
The size of your payout has nothing to do with how well your employer did managing the money. Instead, your payout is simply a function of a basic formula that factors in how long you worked and how much you earned. That is, your benefit is defined by a set formula.
Again, that's about 180 degrees from how a 401(k) works. A 401(k) is a defined contribution plan: You are responsible for investing money from your own paycheck into the plan - sometimes with a matching contribution from the boss - and you are in charge of choosing how you want your money invested among the mutual funds offered. There is no guaranteed payout when you retire; what you end up with depends on how well your investments perform.