At any stage in criminal proceedings against you in court in Ireland, you may decide to plead guilty to the offence.
If you are charged with a summary offence - i.e., one that is to be tried by a judge without a jury, you will plead guilty in the District Court.
The District Judge will then issue your sentence after listening to your legal representative and the prosecution (usually a member of An Garda Siochana - the Irish police force).
If you are charged with an indictable offence - i.e., one that must be tried by a judge and jury, and you decide to plead guilty when you appear in the District Court, you will be required to sign "pleas of guilt".
Before you sign the pleas of guilt, the District Judge will first make sure that you are aware of the facts alleged against you and that you understand the nature of the offence.
You will then be sent forward to the Circuit Court for sentencing. If you change your mind, you may withdraw your pleas of guilt at the Circuit Court and the trial will go ahead.
If you have pleaded "not guilty" in the District Court and you have been sent forward for trial by a judge and jury, you may then decide to plead "guilty" to the offence. If you plead guilty at the Circuit Court, you will stand convicted and the court will then decide your sentence.