There are four options for how pictures are arranged within an album. They are:
You can also control the sort order (ascending or descending) for each of the methods listed above by clicking on the Ascending menu item.
If "Sort Ascending" is checked, the the sort order will display pictures in increasing order (ex. With the Picture date option chosen, newer pictures will appear at the bottom). If ascending is not checked (i.e. descending), then newer pictures will appear at the top.