This word marks a statement because of what was said previously. In this case, Fetus had just said that an accused man should be able to face his accusers and make his defense.
Here "judgment seat" refers to Festus ruling over Paul's trial as judge. AT: "I sat upon the seat to act as judge" or "I sat down as judge" (See: [[rc://en/ta/man/translate/figs-metonymy]])
To "stand trial" is an idiom meaning to speak to a judge so the the judge can decide if a person is right or wrong. AT: "to go to trial about these charges" or "for a judge to decide if these charges against him are true or not" (See: [[rc://en/ta/man/translate/figs-idiom]])