the first 2 are described in the Offences Against the Person Act 1861:
Actual Bodily Harm (ABH) - s. 47 OAPA is one step above assault. This is where the assult has left a minor mark on the victim including psycological injury. So a cut, scrape, bruise, etc. This is because assault can be found where someone touches someone without their consent and ABH is a greater offence, something more. ABH can be caused with or without intent.
Grievous Bodily Harm (GBH) - GBH can either be committed with or without intent. With intent is s.18 OAPA and is worse than without intent under s. 20 OAPA as s.18 is a offence tryable in the Crown Court only whereas s. 20 is an either way offence (Magistrates or Crown Court). Again this is a step up from ABH. It requires the offender to have hurt someone seriously and often interpreted as needing to be life threatening. But can be found where the defendant has broken the skin of his victim. Anything more serious than a minor wound, either physical or mental, will be classed as GBH.
Manslaughter - This is not discribed in any statute. Manslaughter is not something that you can be charged with. Manslaughter is an offence that a defendant will be charged with by the court if Murder either cannot be found, or the defendant is found to have some diminished responsibility (mental incapacity, certain cases of intoxication, insanity etc) in relation to his actions.
Murder - Again not discribed by statute. It is the unlawfull killing of one human being by another. Someone can be tried for murder if they have been found to have caused only GBH and the victim later dies.
Hope that helps
Offences Against the Person Act 1861