Bradley Manning, the US soldier who has admitted to being the source of the massive WikiLeaks trove of classified documents, will address his court martial hearing on Thursday to set out how he pleads to the charges against him. It will be only the second time he has spoken publicly since his arrest in May 2010.

The last time his voice was heard was when he gave evidence last November about his treatment in the military prison at Quantico Marine base in Virginia. He spoke then for several hours about being subjected over a period of months to various forms of suicide prevention.

Thursday's appearance from Manning may be less dramatic – he is unlikely, for instance, to talk about how he was forced to strip naked at night – but it promises to be far more revealing about his thinking and his relationship with WikiLeaks. As the most high-profile leaker – his lawyer's would say whistleblower – in recent times, what he says about how he came to transmit vast quantities of classified information to the anti-secrecy website, and crucially why, could be of great significance.

The format of today's hearing is what is called in military jargon a "providence inquiry". That means he will enter into a dialogue with the judge, Colonel Denise Lind, in which he will enter his plea, while the judge will be seeking to ensure that he understands what he's doing and that his plea is voluntary with no coercion behind it.

Here are 10 things to look out for at the hearing:

1. There will be two types of plea that Manning will be asked about: the charges that he himself has agreed to and to which he is likely to plead guilty, and the charges that the US government alleges against him to which he will probably plead not guilty.

2. The first set of charges are known in military jargon – there's a lot of that in a case like this, so bear with me – as "lesser and included". In plain English, Manning has agreed to plead guilty to a set of charges that are less serious charges than those alleged by the army.

3. In these lesser charges, he is expected to plead guilty to unauthorised possession of various classified documents and videos and "wilfully communicating", ie consciously passing them, to a third party – WikiLeaks.

4. The lesser charges relate to the most famous of WikiLeaks' disclosures – what are in essence a sample survey of the Iraq and Afghanistan war logs, the US diplomatic cables and the Guantánamo files, as well as the 'Collateral Murder' video of an Apache helicopter attack in Baghdad that killed civilians.

5. Unless Manning has changed his mind, he will plead guilty to 10 counts of these lesser charges, each carrying a top sentence of two years. So he is committing himself to a possible maximum sentence of 20 years in military custody.

6. It is highly unusual for an accused soldier to make a "naked plea" – ie one that isn't part of a deal bargain with the prosecution – like this. Some legal experts have questioned why he's doing it. We may learn today more about Manning's thinking – is he doing it because he thinks the forensic evidence from his computers is so overwhelming there is no point fighting the fact that he was the WikiLeaks source, or for some moral reason, or both?

7. By contrast, we can expect Manning to plead not guilty to the major offences the US government alleges he committed. Top of the pile is "aiding the enemy", a count under the Espionage Act that carries a life sentence with no chance of parole. These counts are the ones that will still go ahead in a full court martial trial currently set for 3 June.

8. He is also expected to plead not guilty to the allegations that he stole a US government list of global addresses; that he committed various computer violations that he will argue were widely disregarded in his military unit; and that he transmitted the information to WikiLeaks "with reason to believe that such information could be used to the injury of the United States or to the advantage of any foreign nation".

9. In addition to making clear how he wishes to plead, Manning also wants to tell the court why he did what he did. He has written a 35-page statement which, though we haven't seen it, sounds a bit like a Bradley Manning manifesto. It is not yet clear whether he will be allowed to read it out, but if he does it would go down as a key moment in the history of this complex saga.

10. The other important element to watch out for is anything he says about Julian Assange, the co-founder of WikiLeaks, or Nathaniel Frank, as Assange is believed to have been codenamed in correspondence between them. One of those paying close attention to today's proceedings on that score is likely to be the US Department of Justice, which has convened a grand jury in Virginia to explore the possibility of prosecuting Assange himself.