In order not to get caught up in technical calculations you can use the auto shooting mode. Or can use the TV shooting mode (time priority) as I used to use. This is necessary to be known before you decide to buy Nikon flash.
So I set the speed I want after I set the camera ISO. While the diaphragm will adjust automatically because the TV mode has been locked in the camera system.
After setting the exposure triangle, stay the fourth step of determining the angle of light from the flash to the subject. Why the angle of light that needs to be thought of nothing else because it’s the character of the photo. Frontal light from the front with a reflected first, of course, produces different shadows and textures.
To know the difference I made a simulation on photo model with ISO 800 and speed 1/180. The first and second photos are using the angle of illumination from the front of the model.
The difference, in the first photo, is not coated diffuser so as to produce stronger shadow characters and bright areas more focused on the hands and the range of the nose to the chest. But in the second photo, by adding a diffuser, the light that falls on the subject becomes softer. The shadow is not as loud as the first photo.