The Growth Technology pH buffer solutions are each of a known and fixed pH - 4 and 7 respectively. These can be used to check and calibrate your pH meter, and should be done regularly to ensure accuracy from your pH meter.
Simply pour out a small amount to calibrate, and discard the used solution afterwards to avoid any contamination.
pH buffer 7 will calibrate your meter to neutral. It is recommended to also use pH buffer 4 to calibrate your meter so you have a two point calibration, rather than just calibrating to one level. This just gives more reliability.
Incorrect acidity/alkali levels can damage your plants and stop them from feeding as they should be