A, B, C, D, E, F, G, (H) - doesn't it look like anything? That's right, these are the first letters of the Latin alphabet, which have been used to designate notes and chords for the guitar since the 10th century. A is la, C is do, D is re, E is mi, etc. Please note that the letters H and B denote the same note Si.
Fingering is the chord pattern on the guitar fretboard. The first string is at the top of the image, and the frets are numbered. The red dots indicate on which fret you need to press which string to create a particular chord.
The red line on the fingering means you need a barre for the chord. For example, in the case of an F (Fa major) chord, you will have to press all the strings on the 1st fret of the fretboard with your left index finger.
This is by no means an easy trick - you have to work hard to get the chords to sound. But there is nothing difficult in the barre - a few days of hard training, and Your left hand will acquire the necessary strength. In addition, to make it easier to play at high frets, you can always use a capo - a special device that grips all the strings at the fret of your choice.
When playing the guitar, the technique of sound production is of great importance. As for the left hand, the force should be present only at the fingertips, so you do not need to clench the bar in a fist and strain your hand. And if at first playing the guitar causes you some discomfort, then over time your fingers will get used - and you can better focus on the music.
There are at least two ways to transition between chords. The schematic representation of chords from different notes can be identical with the addition of barre. Note that the base fingerings of the E and F chords are the same except that the second has a barre. The same is the case with the Am chords and, for example, Cm, C, D, etc. Therefore, the first method of transition is that the position of the fingers of the left hand does not need to be changed - it is enough to move it along the neck to the desired place. This approach is used with chord chains, for example, Hm (II) - C#m (IV) - Em (VII), etc. But at the same time, the Em chord can be played in the open position. This is the second way to transition - you have to change the position of your fingers on the neck.
In order to learn how to smoothly change chords, you need to look for the pressure points of the strings that are the same for each of them. For example, when changing from Am to Dm, this will be the A note, which is played at the 2nd fret of the 3rd string. However, as you already know, it's all about regular exercise - after a while your fingers will themselves become in the right frets.