There are, generally speaking, five soil categories:
Light and heavy soils generally differ because of their particle size. Sandy soils, with their granular structure are easy to dig because they are well aerated and very free draining. In sandy soil roots can breathe and because they are not sitting in water they are unlikely to rot or suffer from frost damage over winter. This type of soil will warm up rapidly in the spring, so plants will get off to an early start but because sandy soil loses moisture quickly it is drought prone in summer and a related problem is that soluble plant foods are quickly washed away.
Because clay particles are so fine they stick very closely together when wet. This give a very heavy and difficult soil to cultivate. Digging it while wet can create waterlogging and aeration problems. When dry the clay sets very hard, like concrete.
Adding organic material helps to open the texture and adding coarse grit and sand will improve the drainage.
Loam sits between clay and sandy soil. It is a mixture of fine and coarse particles. It is lighter and easier to work than clay while retaining more moisture and nutrients than sandy soil. Once endowed with sufficient humus this is th best garden soil.
Peat soils are organic rather than being based on mineral content. It is composed from many years of decomposed plant matter. Peat soil is prone to waterlogging so you need to add coarse grit and sand to alleviate this problem.
Chalk soils are generally shallow, stony and free draining. So chalk soils drain very quickly and lose nutrients. This type of soil benefits more from feeding than any other type of soil.
To improve water retention dig in organic matter and by mulching. Over the years, as you dig in more and more organic matter the soil will darken and get richer. Vegetables prefer well cultivated chalky soils and the lime helpsto prevent cabbages from getting club root.