How to make two actors detect overlap?(At the beginning of the scene)

How to make two actors detect overlap?
请问 如何 让 两个 actor 检测 重叠?
(At the beginning of the scene,not later to do )
(在场景一开始)
(My English translator to ask the question…sorry about that)
(我用的 英语翻译器 来问的问题…)