How to use Guitar tuner! Do you know what the following letters mean?

In standard tuning, just turn the letter to “g”, which means guitar. Then, every time you play any string, new letters appear on the tuner, which correspond to EADGBE from six to one (the coarsest to the finest). For special tuning, go to “c” file, which means twelve average, and then find the corresponding sound. Why is it that I tune one tone and then the other tones and then go back to tune the first tone differently? After playing, the string button is offset, which makes the pitch deviate. What’s the way to do this? Always tune it? The answer is right. But if the pitch always deviates too much, consider changing the knob or guitar.