Start by collecting soil samples from different areas in your garden.
Put about 2 spoonfuls of soil into different containers.
Add 1/2 cup vinegar to the soil. If it fizzes, you have alkaline soil, with a pH between 7 and 8.
If it doesn't fizz, add a little bit of distilled water to the other container of soil – just enough to make it muddy.
To that, add 1/2 cup of baking soda. If it fizzes, you have acidic soil, with a pH between 5 and 6.
If the soil doesn't react to either vinegar or baking soda, you have neutral soil (which is the best soil to have!).