I'll try

In criminal law there are two types of burdens of proof: evidential and legal.
You must first prove the
evidential burden - that there is sufficient evidence for an issue to go before a jury. I believe this is raised at the committal hearing, where there is only a judge and no jury. Here the judge decides what issues will be put to the jury (so the jury's/court's time is not wasted with issues which do not have sufficient supporting evidence)
Only then does the
legal burden arise: prove the issue itself to the requisite standard. This happens at the actual trial (often, but not necessarily always, with jury).
For the elements of the crime:Prosecution has discharged its evidential burden if it has proved, merely
on the balance of probabilities, that there is sufficient evidence.
However, then prosecution only discharges its legal burden if it has proven beyond reasonable doubt that the elements of whatever crime is in question are all present.
For the general defences such as self-defence:Defendant merely has to prove that there is evidence of such a defence
on the balance of probabilities.
Legal burden is then on prosecution - i.e. has to prove beyond reasonable doubt that there is no defence.
For what are called affirmative defences: (includes mental impairment [formerly insanity] and express statutory exceptions)Both the evidential AND legal burden are on the defendant, but they only have to prove both on the balance of probabilities.
sorry for the ramble, but I do love criminal law ... except when I'm being examined on it