Rule is a common feature offered by a desktop-based email client app. You can use this feature to filter emails by certain criteria such as sender, subject, or email that contains certain words on their body. You can then make a certain action over the filtered emails such as send them to the spam folder, delete them, flag them, and so on. Microsoft Outlook, the popular desktop-based email client app for Windows and Mac, also allows you to create rules.
Rules are great to manage emails. You can, for instance, create a rule to automatically send emails from a certain sender you consider it a spammer to the spam folder. Or, you can create a rule to send all newsletters to a Newsletter folder to prevent your main inbox from getting overflowed by unfiltered emails.
How to create a new rule in Outlook
To create a new rule in Outlook, click the File menu and select Manage Rules & Alerts. This will open the Rules and Alert window.

On the Rules and Alert window, click New Rule to open the Rules Wizard.

Select an action you want to make to the filtered emails on the Stay Organized section. For instance, if you want to send emails from certain senders, you can select the top option (Move messages from someone to a folder). Or, if you want to send emails that contain certain words in the subject to a certain folder, you can select the second option (Move messages with specific words in the subject to a folder). In this example, we select the first option.

After setting an action, click the underlined texts on Step 2 box. First, click the people or public group text to add the email addresses you want to apply the rule to.

If the email addresses are already available on the list, you can double-click them to add them. Otherwise, you can manually type the addresses on the From field. To add multiple email addresses, you can separate them with a semicolon. Click the OK button.

Next, click the specified text to select a folder you want to send the filtered emails to.

Select an existing folder and click the OK button.

Click the Next button three times until you see the following step and click the Finish button. By default, your new rule will only be applied to the upcoming emails. If you want to apply the new rule to the existing emails — in the Inbox folder — you can tick the Run this rule now on message already in “Inbox” option before clicking the Finish button.

You can click the New Rule button to create another rule. Once done, click the OK button to close the Rules and Alert window.
There is also an instant way to apply a rule to an existing email. Simply right-click an email in the Inbox folder (or any folder) and select Rules -> Create Rule.

Set an action from the available list on the Do the following section. You can also click Advanced Options to open the Rules Wizard.

How to edit and delete the existing rules
To edit or delete the existing rules, you can switch back to Files -> Manage Rules & Alerts to open the Rules and Alert window. Double-click a rule to edit it. To delete a rule, select a rule you want to delete and click the Delete button.

Click the OK button to close the Rules and Alert window.