it simple one u have assigned the end points fillet radius then it will gradually change the fillet radius. a small tutorial.
select the the edge or face that you want to fillet and select variable fillet in in the manual tab in the fillet feature.
Then select the number of points where you want to change the fillet radius.
here i chose 6.
first fix the values of the end points of the edge.
by selecting the end points.
then select the points on the edge and change the fillet radius in the "radius" option of the variables radius parameters
then click ok to get the finished product.