After you arrive on campus, you choose courses to visit during the course selection period.

开学以后的选课阶段, 你可以随意选择去参加哪些课程。

It is Yale's course selection period during the first two weeks of classes which allows you to participate in courses that interest you without enrolling in them right away.

所谓的选课试听阶段指的是新学期伊始前两周的试听课阶段，这时你可以选择去试听自己感兴趣的课程, 而不用马上做出决定最终是否选修这门课程。