Eamon Bradley, 28, from Melmore Gardens in Creggan is accused of receiving weapons training at a rebel camp in Syria in 2014.
He was arrested after returning home later.
On Wednesday, the jury at Londonderry Crown Court was read transcripts of his interviews with the police.
He told police after training with a rebel faction called the Army of Islam he took part in three battles, two against government forces and one against ISIS near the city of Aleppo.
But he said he never used his AK47 or grenade on the battlefield. He became disillusioned with the fighting and returned home.
Earlier, the trial heard that Mr Bradley contacted people on social media to help him get into the country to join the rebellion.
Mr Bradley, a Muslim convert, denies six charges, including attending a rebel training camp in Syria and receiving training in guns and grenades.
The case is the first of its kind in Northern Ireland.
Mr Bradley told police he got a bus from Derry to Dublin in February 2014 after meeting a contact on Facebook.
He then flew to Istanbul and got a second internal flight to Adana, in southern Turkey, where he made contact with sympathizers through the mobile messaging service, WhatsApp.
He told detectives he travelled near the Turkey/Syria border but he was warned to go no further because it was controlled by so-called ISIS.
Mr Bradley said he stayed with a man in a nearby village who he believed had contacts with the Free Syrian Army.
Asked why he was travelling to Syria and if he had any concerns, he told detectives: "I just wanted to be among the people who were being bombed".
He added that he had no concerns because he "trusted in Allah".
Mr Bradley said he spent about two months in the village before a group of men, who claimed to have been held captive by ISIS, helped him cross into Syria on a makeshift raft.
He then joined a mountain training camp belonging to the group Jaysh al-Islam - the Army of Islam.
Detectives were told that it was here that he learned to fire AK-47 rifles and Russian machine guns; he also received some instruction on the use of mortar bombs.
Mr Bradley told police that he was the only western European at the camp and was on the bottom rung of the ladder when it came to the group's command structure.
The trial continues.
A Derry man accused of terrorism in Syria told detectives that he never fired a single shot against the enemy in his whole time there.