When you mix hot water and coffee powder you get what will loosely resemble brewed coffee.
Coffee powder is just dehydrated coffee also known as instant coffee.
The taste of instant coffee or coffee powder mixed with hot water also has a different taste and does not taste as good as fresh hot brewed coffee from regular coffee grounds do.
When making instant coffee, you mix coffee powder with boiling water to extract the flavor and aroma compounds from the coffee.
The high temperature of the boiling water helps to dissolve the coffee powder and release the soluble coffee compounds into the water.
You can also mix ground coffee in hot water but it won't be as good as brewing it in a coffee pot.
In a deep bowl, add 1 tablespoon of coffee grounds for every cup desired.
Pour boiling water over the grounds.
Pour a little boiling water over the grounds to saturate, and then add the amount of water needed for the intended number of servings. Pour brew into a mug.