You can create reorder points for a specific variant or in bulk:
For individual variant
Go to the Inventory section. Select the product, and click on the variant you want to edit.
Make sure you have "Manage Stock Levels" Checked on your Details tab in the Variant popup.
Go to the Stock Locations tab.
You can set the Reorder Point column on any row, each row corresponding to a single location.
Save the changes.
The variant has now been updated and the stock reorder point per-location is now set.
To find out which of your items needs reordering go to the Intelligence section of your account and run a reorder report.
Create reorder point(s) in bulk
You can only create reorder points in bulk by location. To do so, you have to export location data, edit the spreadsheet accordingly and re-upload it. Follow the steps in this article.