Child with RoA-CoE

Dear members,
I am British (by Naturalisation). My 18 months old son has an ROA-COE in his pakistani passport. He
has arrived in the UK with his pakistani mother (who is on UK dependant visa) a week ago.
Now I wish to apply for his British Passport.
Could someone guide me through please,
1) where to start from?
2) which application to fill in?
3) what evidence to provide?

Advance appreciations

Thank you CR001,
This guidance quotes that "Your child must have British nationality to be eligible for a British passport".
He has a pakistani passport at the moment.
Do I need to register him as "British Citizen" first, get the certificate & then apply for passport?
Also, do we need to attend citizenship ceremony etc ?

If you were British by naturalisation before you son was born, then he is automatically British. Include the same evidence as when applying for CoE-RoA.

Thank you so much both of you sirs.
This website has really helped me during the last 7/8 years..
Thank you for the extraordinary help & commitment..