The sort criteria for items is set at the parent. If you want certain products to show in a particular order, you must set this at the parent category of those products. First you set the criteria by which products will be sorted:
Sort Products By :
Product ID
Product Name
Product Creation Date
Product Last Modified Date
Product Category Sort
The last one of these should be selected if you wish to manually sort the products into exactly the order you required.
You also need to set a sort direction:
Ascending
Descending
For example, sorting by 'Product Last Modified Date' and sort direction 'Descending' will show the most recently edited/added products first.
To manually sort the products, you must first set the category
to sort products by 'Product Category Sort'. You will then see up/down
arrows appear on the products when viewed in the back end, as shown
below. You can click these to sort the items.
Alternatively, from v2.9014 onwards, you can also drag and drop sort too.
If sorting products manually ("Product Category Sort"), make sure you select the direction as 'ascending'. It won't work correctly if set to 'descending' as the code that tries to find the item above or below to swap with will find the wrong value.