The General register Office Index has been transcribed by ancestry.co.uk to make it wasy to search for a specific birth. You will be able to look at the transcribed index under the name you want and what you see on the screen is the childs name a month and year which tells you which quarter of the year the event took place, as the registration year is divided into 4,jan feb mar.apr may jun/jul aug sept/oct nov dec.
then you will have the name of the registration district and a vol and page number from the original register.
In later indexes from about 1911 the mother;'s maiden name is included.
Once you have found a possible birth on ancestry that is useful and you think may be the one you want, you then can use that information to order a certified copy of the birth registration from the lkocal register office or ancestry.co.uk thenselves. the thing about the local offices is that iot only costs �7, but you would need to get the address etc, but that's easily done online.
Once you get the birth certificate you should get the date and place of birth, the childs christian name if ealry or the childs christian name and surname of later. the name of the mother and usually father, the occupation of the father, and later the mother,
i would also add that if you are still learning how the sources work you may want to go to your local library and use ancestry.co.uk library edition for free whilst you get used to how it works, rather than spending alot of money learning how it works and wasting your money.