Since there are many different testing kits and tools on the market, the short answer is that you should read the documentation that came with the test kit that you purchased. Some kits are quite sophisticated, akin to the chemistry set you may have had as a child. The four basic tests performed by most home test products are pH, nitrogen, phosphorus, and potassium.
I suggest you create a map of your gardens and yards, and then test samples from various locations, recording the results on the map in the area that the test was performed. When you are done, you will have a good visual representation of what areas are healthy and which ones need amending to improve fertility. You can then use the information provided with the kits, or another data source, to add the necessary amendments.