Decide where on the house’s soffit you wish to install the vent. Measure the back of the soffit vent, or the part that inserts into the house, and then climb a ladder and draw the same dimensions on the soffit.
Cut along the lines you drew on the house’s soffit with a jigsaw. Insert the soffit vent into the cutout and mark where the vent’s anchor holes sit on the soffit. Remove the vent, drill pilot holes where you marked, and then replace the vent and drive screws into the holes you drilled to hold the vent in place.
Climb into your house’s attic and located the bathroom ceiling fan. Slide a duct elbow onto the fan’s exhaust port and drive sheet metal screws though the elbow and exhaust port lip to hold them together.
Slide adjustable clamps over the ends of a flexible duct hose. Insert one end of the hose over the open end of the duct elbow and use a screwdriver to tighten the clamp so the hose sits securely on the elbow. Slide the other end of the duct hose over the exhaust opening in the soffit vent from inside the attic, and then tighten the clamp.