Many edible plants are typically grown from seed but some are usually grown from baby plants, often because growing them from seed takes a long time or is unreliable. There are different names for different types, for example:
Onions can be grown from miniature onions known as sets. These mature faster and are less prone to disease. Check the variety to see if they should be planted in autumn or spring.
Garlic is generally supplied in large bulbs made up of many cloves. Each individual clove can be planted to produce a new plant. Check the variety to see if they should be planted in autumn or spring.
Potatoes are grown from miniature potatoes known as seed potatoes and are generally split into three groups: first earlies, second earlies and main crop (depending on when you harvest them). To get them off to a good start, they are chitted before planting which allows the growing shoots to develop.