Using a brush is a pretty basic skill. It's all a matter of using the proper amount of water with your particular brush matched to the amount of water you need for the soap you are using and then some twirling to develop the lather. So you have to experiment with the water. What can complicate things are having hard water and a brush that fights you. If you have a brush that is stiff it needs to be softened , usually by soaking and being broken in especially if it is a new boar.

You got plenty of good advice here so I would just do some practicing and change the variables.