A pinch is when you pinch two strings between your thumb and 1^st finger. You can also pinch between your thumb and middle finger and even the ring finger. Let’s try it. All examples below are using a G chord. Use a metronome. Focus on thumb independence.

     i             i             i             i
     p  p  p  p    p  p  p  p    p  p  p  p    p  p  p  p 
E------------------------------------------------------------
B------------------------------------------------------------
G----0-------------0-------------0-------------0-------------
D------------------------------------------------------------
A------------------------------------------------------------
E----3--3--3--3----3--3--3--3----3--3--3--3----3--3--3--3----
     1  2  3  4    1  2  3  4    1  2  3  4    1  2  3  4

Move the pinch to the 2nd beat.
        i             i             i             i
     p  p  p  p    p  p  p  p    p  p  p  p    p  p  p  p 
E------------------------------------------------------------
B------------------------------------------------------------
G-------0-------------0-------------0-------------0----------
D------------------------------------------------------------
A------------------------------------------------------------
E----3--3--3--3----3--3--3--3----3--3--3--3----3--3--3--3----
     1  2  3  4    1  2  3  4    1  2  3  4    1  2  3  4

Move the pinch to the 3rd beat.
           i             i             i             i
     p  p  p  p    p  p  p  p    p  p  p  p    p  p  p  p 
E------------------------------------------------------------
B------------------------------------------------------------
G----------0-------------0-------------0-------------0-------
D------------------------------------------------------------
A------------------------------------------------------------
E----3--3--3--3----3--3--3--3----3--3--3--3----3--3--3--3----
     1  2  3  4    1  2  3  4    1  2  3  4    1  2  3  4

Move the pinch to the 4th beat.
              i             i             i             i
     p  p  p  p    p  p  p  p    p  p  p  p    p  p  p  p 
E------------------------------------------------------------
B------------------------------------------------------------
G-------------0-------------0-------------0-------------0----
D------------------------------------------------------------
A------------------------------------------------------------
E----3--3--3--3----3--3--3--3----3--3--3--3----3--3--3--3----
     1  2  3  4    1  2  3  4    1  2  3  4    1  2  3  4

Try a pinch with an alternating bass line.
     i             i             i             i
     p  p  p  p    p  p  p  p    p  p  p  p    p  p  p  p 
E------------------------------------------------------------
B------------------------------------------------------------
G----0-------------0-------------0-------------0-------------
D------------------------------------------------------------
A-------2-----2-------2-----2-------2-----2-------2-----2----
E----3-----3-------3-----3-------3-----3-------3-----3-------
     1  2  3  4    1  2  3  4    1  2  3  4    1  2  3  4

Move the pinch to the 2nd beat.
        i             i             i             i
     p  p  p  p    p  p  p  p    p  p  p  p    p  p  p  p 
E------------------------------------------------------------
B------------------------------------------------------------
G-------0-------------0-------------0-------------0----------
D------------------------------------------------------------
A-------2-----2-------2-----2-------2-----2-------2-----2----
E----3-----3-------3-----3-------3-----3-------3-----3-------
     1  2  3  4    1  2  3  4    1  2  3  4    1  2  3  4

Move the pinch to the 3rd beat.
           i             i             i             i
     p  p  p  p    p  p  p  p    p  p  p  p    p  p  p  p 
E------------------------------------------------------------
B------------------------------------------------------------
G----------0-------------0-------------0-------------0-------
D------------------------------------------------------------
A-------2-----2-------2-----2-------2-----2-------2-----2----
E----3-----3-------3-----3-------3-----3-------3-----3-------
     1  2  3  4    1  2  3  4    1  2  3  4    1  2  3  4

Move the pinch to the 4th beat.
              i             i             i             i
     p  p  p  p    p  p  p  p    p  p  p  p    p  p  p  p 
E------------------------------------------------------------
B------------------------------------------------------------
G-------------0-------------0-------------0-------------0----
D------------------------------------------------------------
A-------2-----2-------2-----2-------2-----2-------2-----2----
E----3-----3-------3-----3-------3-----3-------3-----3-------
     1  2  3  4    1  2  3  4    1  2  3  4    1  2  3  4

What if there were multiple pinches per bar?
     i     i       i     i       i     i       i     i
     p  p  p  p    p  p  p  p    p  p  p  p    p  p  p  p 
E------------------------------------------------------------
B------------------------------------------------------------
G----0-----0-------0-----0-------0-----0-------0-----0-------
D------------------------------------------------------------
A-------2-----2-------2-----2-------2-----2-------2-----2----
E----3-----3-------3-----3-------3-----3-------3-----3-------
     1  2  3  4    1  2  3  4    1  2  3  4    1  2  3  4