pH is the measure of acidity or alkalinity.
A neutral pH of 6.5 is generally considered considered best for growing most garden plants.
Ericaceous plants, like rhododendrons and blueberries, prefer slightly more acidic soil.
There are also some diseases which are effected by soil pH.
Knowing your soils pH can help you make better decisions about your garden design.
This is all about the ratio of silt to sand to clay.
There's no such thing as a 'bad' soil. Each has it's advantages and disadvantages.
A very clay soil for example, may be heavy and difficult to work but it also holds nutrients well.
Knowing your soils texture will help you work with your soil.
Many nutrients support healthy plant growth. The major nutrients are Nitrogen (N), Potassium (P) and Phosphorus (K).
A deficiency of any of these elements can cause serious problems in your garden.
Macro nutrient deficiencies are fairly rare in gardens. A problem which exhibits as a major nutrient deficiency is more likely to be caused by something inhibiting nutrient uptake.
However deficiencies are more likely in some soil types and with some horticultural practices.
Knowing more about your nutrient levels can help you identify and resolve problems with your soil.