Use the stud finder to locate the eave studs beneath the soffit board and mark each one. You need to install the vents between the studs.
Make a cardboard template of the vents about ½ inch smaller on all sides than the actual vents. Hold the template up to the soffit board between the studs and trace it.
Poke two holes in the opposite corners of the traced vent holes with the jigsaw, and then cut out the soffit vent opening using the jigsaw.
Position the soffit vent over the vent hole with the vent louvers facing the house. Place screws into the holes in the sides of the soffit vents and use the screwdriver to tighten them in place.