Groom already gave you the link to the GRO site for ordering certificates - you just have to register. Don't know what English certificates you want to order but if one is the death certificate of Tacy that I'd previously mentioned the details you'll need are:
Tacy Sara O'Neill - age at death 62
Year of death - 1976
You'll be asked if GRO Index Reference known - 'Yes'
Quarter - September
District name - Salford
Volume no. - 39
Page no. - 0924
Glad that Sinann gave you details for ordering the Irish certificate as I knew nothing about ordering certificates in Ireland.
One piece of advice - when you order the specific certificates (or indeed any other certificates) always enter the name details exactly as spelt in the indexes i.e. marriage of Tacy in Ireland gives her name as Tacey Sarah Rocliffe and her death in England is as Tacy Sara O'Neill.
Let us know when you eventually receive the certificates and what information they contain and we'll endeavour to help you further.
Good luck.
Annette