Soba noodles are made of mixture of buckwheat, flour, salt and water. Depending on the ratio of buckwheat and flour, they are referred as towari (buckwheat 100%) or nihachi (buck wheat 80% and flour 20%). According to Japanese wiki, buckwheat contents has to be at least 30% in order to be labeled as soba, and at least 50% to be labeled as high grade.
When I was a child, my grandma used to buy 100% ground buckwheat. She took about 1/2 a cup of it in a bowl and mixed it with a little amount of boiling water to make paste. I picked a bite size soba paste with chopsticks, dipped it into soy sauce, and ate. It was very flavorful with a small amount of soy sauce. She added finely chopped scallion and shichimi pepper in the soy sauce to adjust the taste more palatable for her.
Soba is dried when sold at stores. The noodles are boiled and rinsed under cold water to get the bite and tight texture. After rinsing and draining the excess water in colander, soba can be prepared hot or cold. The boiling water can be reserved and offered as sobayu, which will be added to leftover noodle soup to drink.
Many toppings can be added on soba noodles. Shrimp tempura is one of my favorite on hot soba noodle soup, it is great to add nameko mushrooms, or stewed abura-age (deep fried tofu). During hot and humid summer time, dipping cold soba noodles in cold noodle soup is refreshing.
American health food restaurants or delis sometimes offer salad that contains soba noodles. It is known that buckwheat has an effect to cleanse digestive system. Therefore, it is a good idea to eat soba time to time.
Soba noodles can be found at Japanese grocery stores, other Asian grocery stores, or health food stores. For ordering online, here are some of my suggestions;