By default the items displayed in a view are sorted by their backlog priority. There are cases when you might want to see them ordered differently. For example, you can order bugs by create date to see which are the newest (or oldest) bugs logged.

Use the sort button…

…and pick the property to sort by:

Or if you are in a list view, you can click on the column headers to sort by that column. 

Sort board rows

When you are in board view by Parent items, you can apply different sorting for the row items. You can sort by any field just like the items sorting.