The baseline Monk class is very weak so this powerful feat is intended to give them some base power and options.
You've fully mastered the flow of unarmed combat, when in combat you regain 1 Ki point at the start of your turn.
Deflect and Counter (replaces Deflect Missiles)
When you are hit by a weapon attack, you can use your reaction to enter a defensive stance until the start of your next turn. While in this stance you can attempt to deflect a number of weapon attacks equal to 1/2 your proficiency bonus. When you do so, the damage of the attack is reduced by an amount equal to twice your monk level.
If you reduce the damage of an attack to 0, you can spent 1 ki point to attempt to counter the attacker with an unarmed strike as part of this reaction. If the attack was made by a ranged weapon, you can catch the missile if it is small enough for you to hold and have at least one hand free. If you catch a missile in this way, you can use it as part of a counter attack. The missile is treated as a dart for the purposes of determining range and damage for this attack. Once you counter an attack, you can't do so again until the start of your next turn.