In the Backlog board, you can assign different priorities to different User Stories. The position of the User Stories on the board is also respective to their priority as compared to other User Stories.
Firstly, you can move a User Story up and down the backlog board by pressing the number button to the left of the User Story Title.
Secondly, you can change the priority level of a User Story by using the star system of priority. User Stories can be rated from 1 to 5 stars, with 1 star being the lowest priority and 5 stars being the highest priority.