A pension is a "defined benefit" plan that the employer provides based on a formula that includes years of service and your earnings history. You can contact your Human Resources department which should be able to provide you with any contact information as well as the formula to be used.
Any pension estimate for a younger worker is really based on a number of assumptions: how long you work at the company, your projected earnings growth, the company's contribution and investment performance.
If you are looking to "cash out" of your pension and receive a lump sum or do some sort of rollover to another qualified account like an IRA, that's not going to happen. In rare instances, an accumulated benefit may be available for "rolling over" but that typically is for a minimum time period at the company and a minimum amount.
Yes contact the HR dept. of the employer. But if you have a 'cash balance' defined benefit plan and you have left the company, you can do a direct transfer to an IRA without tax consequences if done properly. If you have a traditional defined benefit plan that provides a monthly benefit, see Steve's response for your options. Also be aware if a traditional plan and you left the company, the monthly benefit estimate provided typically reflects actual dollar amount received at retirement age (typically 65 but check your plan). This amount most likely will not be adjusted for inflation. Again, check the assumptions closely but at your young age, you will need 2.2x that dollar amount at age 65 to have the same purchasing power (assuming a 3% inflation).