There are three ways to import brush tips in the form of AFBRUSHES files into Affinity Designer: (1) Double-click on the brush files in AFBRUSHES format. (2) Drag and drop the files into the program. (3) In the Brushes panel, select Import brushes from the menu in the top right-hand corner.
Using brushes in Affinity Designer for free-form drawings and as an outline
To draw freeform shapes, select the paint brush and a desired brush tip. To apply the brush tips as outlines, select a graphic object and apply the desired brush as an outline by clicking on it. You can use the Width parameter to set the strength of the brush effects.