You typically don't fork over any of your paycheck to participate in a defined benefit plan. Your employer does. But you do have to put your own money into a defined contribution plan like a 401(k) or a 403(b). Obviously, a defined benefit plan is a much better deal for you.
Because defined benefit plans are more costly for employers than defined contribution plans, most of them have - you guessed it - scaled back dramatically or eliminated these plans altogether in recent years. If you still have a defined benefit plan at your company, consider yourself lucky.
Some employers offer both defined benefit plans and defined contribution plans. If yours does, you should definitely participate in the defined contribution plan as well. That's because a defined benefit plan on its own likely won't be generous enough to let you live comfortably in retirement.