Pinching back sounds like it would hurt doesn't it? I remember getting pinched when I was younger and it usually meant I had done something to deserve it. It sure didn't help me grow, even though I did learn not to do whatever caused the pinching again. Even so, I did grow, didn't I?
As counterintuitive as this sounds, pinching back plants can actually produce more flowers and even more foliage on a plant. It helps the plant to put out energy on new growth. To pinch back, you will want to make sure that the plant is at least 2-4 inches tall.
I will use Petunias as an example as I look forward to pinching them back every year and seeing the new growth and flowers appear. To pinch back I would locate a new shoot and pinch it back at the center of the stem between the leaves.
Just take your fingers and pinch it off. The pinching will not only cause the plant to fill out but will also cause more blooms.
For me, that's why I enjoy it because I know how it will improve the plant in the long run. If I don't pinch back, I will have long stems with few flowers that will straggle over the sides of the pots. Still pretty, but not as pretty as it can be.
You can also pinch back your vegetable and herb garden to produce more yield.
Many plants that do very well with pinching back are Petunias, Chrysanthemums, Coleus, Hosta, Tomatoes, Herbs, Lettuces and many more. I think you'll find it a fulfilling, productive and enjoyable thing to do. Happy pinching!