What it means
Examination-in-chief is the first stage of a witness's oral evidence, conducted by the party who called that witness. Its purpose is to draw out the witness's account of relevant facts. As a general rule the questioner cannot ask leading questions on contested matters. In many civil cases evidence-in-chief is given in advance by affidavit or witness statement, with the witness then made available for cross-examination.
How it's used
During examination-in-chief, the plaintiff explained how and when the goods were delivered.