To beat until fluffy means to beat the ingredients until it's lightened in color from it's tiny air bubbles.
An example of beating until fluffy is to start by beating the fat (room temperature) well and then gradually add the sugar until the mixture does get light and fluffy.
The difference between whisking and beating is the beating is done to mix the ingredients thoroughly and whisking is to incorporate air into whatever is being whisked.
To whisk you can use use a hand whisk which is a cooking utensil that can be used to blend ingredients to smooth and to incorporate air into a mixture, in a process known as whisking or whipping.
Most whisks consist of a long, narrow handle with a series of wire loops joined at the end.
Beating ingredients means to rapidly stir the ingredients to mix the ingredients thoroughly.
Beating ingredients can be done with either and hand mixer, electric stand mixer or other mixer or even a fork.
You can take a few forks together and use them to beat ingredients with such as beating egg whites to stiff peaks.