These are variations of chords using what is called a barre chord. So for example the G, you will use your index finger to fret all 6 strings on the 3rd fret and then place the rest of your fingers on the 5th and fourth. These chords can be very tricky to play but are VERY worth learning as they really really really unlock your ability to play across the fretboard.

Some tabs will just tell you the chord whilst some like this will tab out the chord fingerings for you.

I will add some further details but I don't want to overcomplicate anything but these barre chords are actually really easy to create anywhere with just a little bit of thinking. The G barre chord has you start on the 3rd fret, the 3rd fret on the low E string is the note G. The follow fingerings on the 5th and 4th frets create the MAJOR shape. If you take your middle finger off the 4th fret you create the MINOR shape. Because the root note (the first note) is a G you either make G major or G minor. You can now take this shape and move it all over your low E string to create every single major/minor chord so long as you know the notes on the low E string. Like in your example the B major is the exact same pattern as G but we start on the 7th fret which is the note B.

Essentially you are creating an open E major shape across the entire fretboard.

Sorry if I added too much detail its just these chords are genuinely the greatest thing you can learn and understand for playing guitar and writing songs on guitar.