Most of the filters have the same dialog. You can set the Size of the filter matrix. This value controls the effect of the filter and is dependent of the desired effect.
With Channels you can choose the color space and the color channel, which you want to edit.
Some filters have a slider named Threshold. Most of the time it controls a limit, at which the filter starts working. The exact meaning is depending on the filter.
The slider Intensity controls the intensity of the filter. This way you can reduce the effect of a filter on an image very flexibly.
Further description on using the dialogs can be found in chapter 3.9 "The Parts of a Typical Dialog".