1: Whisk
Made up of lots of thin metal wires, this is mainly intended for whipping, to liquefy, mix and, above all, incorporate air with its rapid movement. Typical examples:
beating egg whites or
whipping cream.
So this is a tool that needs to turn at high speed, in mixtures that are very fluid, to be most effective.
2: Flat beater
This beater has a flat "paddle" shape, hence the name, and is intended for thorough, even mixing. Typical example:
cake batter.
It needs to run at slow or medium speed in mixtures that can be either fluid or moderately thick.
Note: In Kenwood terminology, this tool is called a "K beater".
3: Dough hook
In the form of a single metal arm shaped like a sort of twisted hook, this is intended for kneading firm doughs. Typical examples:
bread or
brioche dough.
It needs to run at the mixer’s slowest speed possible so as not to spoil the dough.
To sum up : With these 3 tools you can do practically everything you need for cooking, or baking bread, cakes and pastries. You just need to choose the right tool for the job.