Six Strings, E-A-D-G-B-E, and Tuning Before Every Practice
With the guitar resting on your lap, the thickest string sits on top. It is called the sixth string and is tuned to low E. Counting down from there you have the fifth string on A, the fourth on D, the third on G, the second on B, and the first and thinnest string back on E, this time high E. That E-A-D-G-B-E order is standard tuning, used by almost every beginner song, and its reference pitch is A at 440 Hz, the international standard pitch set by ISO 16. Wood and strings drift with temperature, humidity and tension, so yesterday's tuning may already be off today.
The friendliest tool for a beginner is a clip-on tuner fixed to the headstock. It reads vibration straight from the wood, which keeps it accurate even in a noisy room. A phone tuner app works as a backup as long as the room is quiet enough for the microphone. Set the tuner to chromatic mode (usually marked C), pluck with steady, moderate force, and turn the peg in small moves; a quarter turn already shifts the pitch a lot. Try to reach each target note from below. If you overshoot, slacken the string past the note and bring it back up slowly, because a string tuned upward holds its pitch better. Cranking far beyond the target can snap the string.
Tuning one string changes the tension on the whole neck, so strings that were right a minute ago can slip. That is why all six get a second and often a third pass, especially new strings, which keep stretching for the first few days. Once the tuner feels routine, the ear can start learning through the fifth-fret method: press the sixth string at the fifth fret and match it to the open fifth string, then repeat for each neighbouring pair. One exception is worth memorising. The third string to the second uses the fourth fret.
A guitar checked at the start of every practice trains the ear on correct pitch from the very first chord.