The position arrangement is displayed by default when you access any category. Products are sorted in order of newly added products first to newest when you select in any category.
But you can change the position of those products in order by changing position. Check out the following guide to learn more.
When you change the position by selecting Position and pressing the up or down arrow direction the products will not change.
Please login to your admin and follow the following path : Admin panel > CATALOG > Categories > the category you want to modify > Products in Category . Here we will take any category to show this example:
Next, click Products in Category to display the product list.
Here i changed the sort order of 4 products and this is the result displayed on screen.
Good luck