Open an image as shown in section 2.1.1 "Create a simple style using Layer browser". Switch from the Projects pane to the Style Browser, select your first style (e.g. Building Blocks/Geometry/Noise Distortion) and drop it onto the Default Layer. Set the properties in the “Properties + Preview” pane. Now select a second style (e.g. Building blocks/Color Tools/Grayscale). Decide whether to add this second style before or after the first style that you applied and then drag and drop the style into the highlighted area of the layer as shown below. 

Set the style properties in the “Properties + Preview” pane to obtain the effect you want.

Note: See also section 6.3.1 "Quick key combinations in the Compositing view" to add styles quickly and efficiently.
Note: Styles that are dropped either before or after the previous style do not create new layers. The new style appears in line with the previous one on a single layer, like links in a chain. The order of the styles in the processing pipeline can affect the image’s result, so experiment with placing a style before or after another to see what effect the order has on your image.

(click the picture to see the result image)

If necessary, you can still adjust the properties for your image as shown in section 1.3 "Adjust result image properties".