To begin to speak; to start talking (start a conversation or begin explaining).
子どもが突然話し始めて、みんな驚いた。
The child suddenly began to speak and everyone was surprised.
会議で彼が話し始めると、部屋は静かになった。
When he began to speak at the meeting, the room fell silent.
彼女は自己紹介を話し始める前に深呼吸した。
She took a deep breath before she began to introduce herself.
授業が始まると、先生は授業の説明を話し始めた。
When class began, the teacher started explaining the lesson.