Every transaction sitting as Unreviewed is a line the books do not yet explain. The Difference figure at the top — bank minus books — closes as you work through them.
One at a time
For each line: pick a Category, and a Payee if it is a supplier or a customer. Press Post.
Teach it once
After categorising something, press Save as rule. The next transaction that matches is categorised on arrival. This is the difference between an hour a week and five minutes.
Transfers between your own accounts
Money moving from checking to savings is not income and not an expense. Look for the PAIR badge — two opposite amounts on the same day or a day or two apart — and record it as a transfer rather than categorising each side.
What "Filed this way last time" means
It has seen this description before and is showing you what you did with it. It is a reminder, not a rule; nothing happens until you press Post.