The “Deutsche Mark” was introduced as a currency in the German Federal Republic in 1948. The coins could be used as cash until 2001, when they could only be redeemed for the euro.
Not every coin is worth a lot; you should pay attention to special, commemorative and incorrect mintings. Some 5 and 10 mark coins contain 10 grams of silver, as “MDM” writes. The value of old D-Mark coins depends on the year of minting and the condition of the coin.