Pension insurance contributions are 19.6% of gross salary up to €69,000 in Western Länder and €58,000 in Eastern Länder (2013), and split equally between employers and employees.
You don't have to do anything for your retirement/pension and unemployment insurance; both are automatically withdrawn from your income. Pensions are generally paid at the age of 65, but it is also possible to receive an early pension or to work longer and receive the pension at a later age. You get part of it even if you decide to spend your retirement in another country.
The German pension system has come under serious strain during the last decade and is an issue you will see widely covered in the media. Each working generation pays directly for the prior generation's pensions so the system needs to balance payments from current workers with those to pensioners. Low birth rates and increasing life expectancy means less people are financing more pensioners. High unemployment has also reduced payments into the system. Many economists are calling for more immigration of young workers to balance this out.
The pensioner vote has caused German politicians to postpone serious reform for decades. Although the system is not sustainable in its current state, politicians have preferred to pass the problem on the next generation. There is a famous saying of German minister, "Die Renten sind sicher" (the pensions are secured), which today is quoted with cynicism by many who fear for their pensions.
This fear is not irrelevant. Most economists agree that the current working generation will only receive a small fraction of the money it pays in today. To avoid the risk of living on social aid in retirement, you should consider an additional private pension to supplement your potentially low income from the state system. Consumer advice agencies give information on state schemes to fund private and company pension schemes.
For further information, you can contact the Bundesministerium für Gesundheit und Soziale Sicherung (Federal Ministry for Health and Social Security - www.bmgs.bund.de), which has information on pensions, partial pensions, pensions due to reduced earning capacity and pensions due to death (for spouses and orphans).