Why it is a different operation
You are not extracting from a leaf and discarding it — you are suspending the whole leaf, ground fine, in water and drinking all of it. Nothing gets strained out. That means grind quality, water temperature and agitation are the only variables, and it means matcha shows up flaws that steeping would have left behind in the leaf.
Temperature and clumping
Boiling water makes matcha bitter and does it immediately. Around 70-80 °C is the usual range. Clumping is the other constant complaint and is a property of the powder rather than the whisking: matcha compacts in storage and needs breaking up. Sifting it through a small strainer before adding water solves almost every clumpy bowl, and is the step most often skipped.
Whisk, or what else
A bamboo chasen is designed for the job and does it best, moving in a brisk W rather than a circle, and the aim is a fine even foam. Without one, a small milk frother works well and a jar with a tight lid shaken hard works acceptably. What does not work is a spoon.
Grade, and where the money goes
Ceremonial-grade matcha is made from younger shaded leaf and is intended to be drunk with water alone; culinary grade is coarser and more astringent and is intended for milk and sugar to sit on top of. Using culinary grade for a plain bowl is the commonest reason a first attempt tastes harsh and green, and no amount of technique fixes it. The grade names themselves are not regulated, which is a familiar problem.