In a nutshell, you need to apply the filter to a clip byt dragging the filter from the filter palette onto the clip that you want to affect in the Avid timeline, then launch the BorisFX ui by clicking on the little button at the top of the effects window, create the desired effect in BorisFX, and click on the apply button at the bottom right of the Boris timeline window. Then you are back in the Avid UI. You need to render the effect from within Avid. You might want to go to the BorisFX web site, http://www.borisfx.com, if you need help in setting up any of the effects.
I hope this helps.
Peter.