If you have an acoustic guitar, the tuner will have an inbuilt microphone. All you will need to do is place the tuner close to the body of the guitar and pick each string.
Pick each string cleanly. Do not pick the string aggressively as an incorrect reading will be given. Sometimes the needle of the tuner’s meter or the lights will move unevenly and make the tuner difficult to use. This can be caused by several things;