The following details are included on a Birth Cert

     Registration District, County etc
     Date & Place of Birth
     Name (of Child)
     Sex
     Name and Surname and Dwelling Place of Father
     Name and Maiden Surname of Mother
     Rank or Profession of Father
     Signature, Qualification and Residence of Informant
     Date of Registration
     Registrars name

Births were registered from 1864, but some were missed out in the early years.
If the informant is a parent, or relation this is usually mentioned as the qualification - e.g. 'Jane Murphy, Mother, Ballymahon'

Details on a Marriage Cert

     Registration District, County etc
     Name of Church
     Date of Marriage
     Name & Surname of bride & groom
     Ages of bride & groom
     Condition of bride & groom
     Rank or Profession of bride & groom
     Residence of bride and groom at time of Marriage
     Fathers names and occupations
     Name of priest/minister
     name of witnesses
     (plus 'signature' of bride & groom)

All marriages were registered from 1864. In addition to this Non-Catholic marriages, (i.e. Church of Ireland, Registry Office) were registered from 1845.
Age is often entered as 'full', other possible options include an age given in years, or minor if under 21.
Condition is usually one of Bachelor, Spinster, Widow, Widower etc

Details included on a Death Cert

     Registration District, County etc
     Date and Place of Death
     Name and Surname
     Sex
     Condition
     Age at last birthday
     Rank, profession or occupation
     Certified cause of death and duration of illness
     Signature, Qualification and Residence of Informant
     Date of registration
     Registrars name

Deaths were registered from 1864
Condition is usually one of Bachelor, Spinster, Widow, Widower etc
In the case of a married woman or child, the husband/father's occupation is sometimes given - e.g. Theresa Reilly, wife of Farmer
If the informant is a family member this is usually mentioned as the qualification - e.g. on the death of a child 'Patrick Kelly, Father, Dunmore'
In the case of a death in a Hospital, Institution etc - the usual residence (townland or street) is sometimes entered under the name.