Nope. You just need to show up for work. Nice, right? You're automatically enrolled in the plan, though in some instances you need to be on the job for a year before you are officially enrolled. Even though you are enrolled and the pension benefits are being credited to you, they aren't 100% yours until you become fully vested; that can take five or more years.
As for the investment decisions: You have none. Your employer hires a firm to invest the pension plan's assets. There is absolutely no work required (or allowed) on your part to manage the pension money.