Q.My Mango Is About A Month Old And I Want It To Start Branching So It Can Have A Nice Shape And Be Fruitful?
What is pinching a mango plant and what does it do?

Certified GKH Gardening Expert
It is far too young to pinch without knowledge on how to care for a low branching tree! Pinching now will make branching start too low to the soil level, which will invite pests, and disease.
Pinching, or cutting off the very tip of a plant can help structure, but you will want to do this at least 3 or 4 feet off of the ground to make sure that it has enough airflow close to the root zone.
Topping should occur after the first or second year when grown to its full potential. If it doesn't reach 3 or 4 feet by next year, then you may want to look into lighting the tree with horticultural lighting, as it will mean that the tree does not have enough light to grow to its potential.
Pinching this young will be reserved for Bonsai specimens, and will require quite a bit of knowledge on caring for this type of container grown tree, so it isn't recommended if you only have one tree to experiment on.
Here is an article that will help you to care for Mango in container: https://www.gardeningknowhow.com/edible/fruits/mango/mango-trees-in-pots.htm