Touch the pH paper to the sample and match to color of the paper to the pH color chart. A movement of 0.5 is quite easy but, because the pH scale is logarithmic, a movement of say, 2.0 points becomes more difficult because there is a factor of 10x between each full point, so pH 5.0 is actually 100 times more acid than pH 7.0. Also, different soil types react in different ways to the application of lime. To achieve the same result, clay and loam soils require more lime than do sandy soils. There are several common types of lime available for yard and garden use, though care should be exercised with all of the products.
Lime is caustic and a skin and eye irritant and can be dangerous if misused.
If you choose to use such products, carefully read and follow all manufacturer directions exactly. It is very effective to produce a fast change in pH level, and suitable for most heavy clay soils. It is also the strongest form of lime generally available, and you must follow all manufacturer precautions, since your skin and eyes can be easily irritated or burned if the product is misused. How quickly it will act to modify pH and how long it will persist in the soil depends on how finely it was ground. It has the advantage, however, of usually being significantly cheaper than the hydrated lime, and usually woks more slowly and lasts longer.