By default, your Collection items show in the same order as the rows in your sheet. However, you can use Sort to change this order. You can also enable in-app sort so that users can change the sorting themselves.
Default sort
In the Options tab on the right of the Layout Editor, you'll see Sort by Sheet order under Sort Data. You can click on this text to customize how your collection is sorted.
In addition to the default Sheet Order option, this dropdown menu will contain a Random sort and then all the columns in your sheet. Your list will be sorted either Alphabetically or Numerically depending on the data in the column you choose. You can reverse the order of your current sort by clicking the up or down arrows on the right at any time.
Sorting can make more sense of the data in your collections. For example, the app below shows a list of products sorted by price in descending order.