The review tool on the Transactions page allows you to separate your transactions into two statuses: reviewed, and unreviewed.
Think of reviewed transactions as complete transactions, and unreviewed as transactions that still need your attention.
When you import or enter a transaction, it's good practice to ensure that there is a category selected, a sales tax set, any customer/vendor information is added, and the description is correct. Only the category field is mandatory in order to verify the transaction, but make sure you've included everything you need to keep your records accurate.
Once you've checked that a transaction is correct, you can review it.
To review a transaction, click on the checkmark to its right.
You can also mark a transaction as reviewed in the transaction details panel.
Marking a transaction as reviewed doesn't impact your reports, or the ability to perform bank reconciliation. Instead, think of un-reviewed transactions on your transactions page as a to-do list. Take some time to go through your unreviewed transactions and make any necessary changes, before marking them as reviewed.