Hi,
The soil boring plan shows the location where soil boring will be done, often denoted by a small simple symbol with an accompanying alpha/numeric code ( 1, A, or whatever). Often times the boring will be done by a qualified soils engineer or geotech, and the results used to site buildings and/or design appropriate footing/foundations. It's purpose is to get information about the soil composition in different layers sometimes including depth to bedrock.
Many of the CLARB practice questions basically have soil boring plans - the ones that show you soil bore samples have marks A, B, C on the plan, then you look at the 'exhibits' that show a section of what the bore looked like.
Here is a simple example.
Good luck!
Joel