You need to go to the On-Hand Inventory and Alerts card which is in the Inventory dashboard.
If you can't find this card, check if you have moved it to the Hidden Bookmark Cards. If it looks that such card doesn't exist in your account at all, you can easily create a new one, by following these instructions.
Once there you'll need a. to set minimum alert levels per product and then b. search for products needing to be ordered ie those below the alert level (see radio button at top left).
That type of search if done regularly can allow you to keep track of the stock levels of yours that are important to monitor.
If you don't want to do this regularly, you can even get these alerts at your email if you connect Megaventory with Zapier - see here for details.