While executing a Collection, the requests are run in the same sequence as they appear in Postman. Let us have a Collection with at least two requests. To trigger them for execution, first click on the arrow appearing to the right of the Collection name in the sidebar. Then click on Run.
Collection Runner pop-up comes up. The RUN ORDER section shows the order in which the requests shall get executed from top to the bottom. (GET->POST->DEL->PUT). Click on the Run Collection1 button.
Execution Results show the GET request executed first, followed by POST, then DEL finally PUT, as specified in the RUN ORDER.