When it comes to grocery shopping, the options are many in Germany. You can shop from discounters like Aldi, Penny, Lidl and Netto or you can shop from supermarkets like Rewe, Edeka, Real and Kaufland.
Discounters offer groceries with their own brands at lower prices, you can find fine vegetables and fruits and each week discounters reveal Angebot(The discount) theme and offer non-food products at cheaper prices than market prices. Many Germans shop from discounters and follow these Angebot articles so you usually find discounters crowded and discounted items of the week and finest vegetables&fruits run out pretty quickly.
Supermarkets also provide their own brands at cheaper prices (like Ja! brand of Rewe) but the difference between a discounter and a supermarket is that you would find more product varieties in supermarkets. Also, you can find almost any product you want in bigger supermarkets like kitchen tools, home&cleaning products and even furniture.
Prices and quality are indeed a feature of German grocery stores, you can buy fresh products, frozen products and package products with a good quality and cheap price. Fresh products like cheese, whipping cream, sour cream, milk,yogurt and much more that you find in refrigerated areas are really tasty like you would expect from dairy product heaven of Germany. Frozen products like pizza, vegetables and especially fish are also well maintained in their freshness. And packaged products are meeting the expectations like chocolate and sweet products(Although if you value a healthy life they still contain many food additives so I leave that for you to read ingredients and decide).
Bio-products which are offered as organic or healthier can be found in any grocery shops in Germany (look out for bio-tags on products) and there are also bio-shops for these products specifically. They are relatively pricey though.
The thing I appreciate and find really interesting in German grocery stores is that the basic grocery products with a good quality have a price ceiling which enable anyone to buy those at the same prices. For example,in any of discounters or supermarkets you can find one liter of fresh milk for 65 cents, toast-bread for 55 cents, one kilogram of flour for 32 cents, 300 grams of fresh cheese for 85 cents, 1 kilogram cornflakes for 1.99 Euro, a bottle of jam for 1 Euro, 10 eggs for around 1 Euro and so on.. This doesn’t exactly apply to all grocery products like vegetables&fruits but yet again the prices are close to each other for these products in different grocery shops. For purchasing power of Germany, I believe these prices are really cheap.