Welcome back! You've got a great question and I'm happy to go over how the Save feature works on transactions in QuickBooks Online so you can manage your expenses.
The Save button on the program's transactions is a great tool for when you want to save the work you've input so far. I often recommend this button when there's a particularly long transaction to be entered to make sure QuickBooks doesn't time out while you're working. How you've been using this button will depend on where your expenses have gone.
For instance, if you've been hitting Save, closing out of your transactions, and then going back to create new ones, the expenses should all be available for you in the Expenses tab of your books. It may be easier to find the transactions by looking at the individual supplier profiles instead.
If, however, you've been creating an expense, hitting save, and then simply changing the information on the transaction form before saving again, this will have overwritten the work previously done. In order to create separate transactions, it's vital to use the Save and New button or to exit out of the transaction and then create a new one. Re-entering any overwritten work as separate transactions will make sure you've got everything properly recorded.