Roofing question; How to do ridge vent?

[KCM]

I have finished putting the shingles onto my addition. I want now to put on a ridge vent. I have overlapped the felt paper and the shingles. I have not put on the crowning shingles over the ridge yet.

How do I put in a ridge vent at this point? Do I cut open the felt paper and shingles?

[PyroDon]

Leave roughly 2 ft on each end of the ridge covered with the felt and overlapping shingles. Cut both the the felt shingles and decking back 1" on both sides of the ridge before installing the ridge vent . get some 2" roofing nails to install the cap shingles you want them to protrude about a 1/2" through the decking .
Hopefully you got the vent that comes in a roll and looks like layers od plastic cardbord it will give a much cleaner ridgeline , the stuff that comes in 4ft sections is a royal pain