It's pretty straightforward and gives details for each of the registration processes. Please keep in mind that since the amendments were written to cover just about every possible scenario with regards to a child born before 1 July, 2006, to an unmarried British father, you will have to follow the sections that are pertinent to your specific situation. The link to the guidance is in the title below.
Information on how a child can become a British citizen if their father is a British citizen under Section 65 of the Immigration Act 2014.
To give a brief synopsis of all the sections one can apply for citizenship under:
4F - Is for those who could qualify for registration under section 1(3), 3(2), 3(5) or paragraph 4 or 5 of Schedule 2, had their parents been married.
4G - Is for those born after 1 January 1983 who would have become a British citizen automatically had their parents been married.
4H - Is for those born before 1 January 1983 who were citizens of the United Kingdom and Colonies on that date and would have become British citizens if their parents were married.
4I - Is for those born before 1 January 1983 who would have acquired the status of British subject or citizen of the United Kingdom and Colonies and would have gone on to become a British citizen if their parents were married.
So far, if you are applying under section 4F, you will need to pay an application fee. For those who are applying under sections 4G, 4H, and 4I, you will not be paying a registration fee, but you will have to pay a ceremony fee of £80. I'll keep you updated if this changes.