The first port of call for your research should be the Birth, Marriage and Death Indexes.
Using the information gleaned from your relatives you can search for births, marriages and deaths and order certificates of these events from the GRO (General Register Office).
The birth certificate will give you an exact date and place of birth, the father's name and occupation, and the mother's maiden name. The marriage certificate will give the date and place of the marriage, the forenames and surnames of the couple, and their ages (before 1855 it will only show either 'full' if over 21 or 'minor' if under). It also lists the residence and profession of the father plus the names of the marriage witnesses.
You can then use these facts to search the census. Search for the known family members and you will often find the whole family listed with their ages (using our family button). This information can be used to search for further births and marriages, so you can work your way back through the generations. The census will allow you to work back down the tree and help you to find any living relatives.
The Indexes are available to all Premium and Personal Plus Subscribers on the Search page from the main Master Search or in the drop-down box for 'Birth, Marriage and Death Indexes'. For the standard GRO Indexes select 'BMD Records 1837-2005'.