Having trouble forwarding my emails to a specific folder

Open Mail, go to Mail's Preferences (in the Mail menu).

In Mail's Preferences, click the icon for Rules.

On the Rules screen, create a new rule with the instruction to move all mail with the Runner's World "from" address to the mailbox you created for their mail. Save the rule.

If your product info is correct

MacBook (Retina, 12-inch, Early 2015)

I am guessing you misplaced your question in the Classic Mac OS forum.

If you will post back with your correct OS X version - we can get this moved

If indeed you are asking about a Classic OS Mail app, we'll leave it alone 😉

BTW, Don's answer is spot on and easy to follow.

The item "Any recipient"

is a pulldown menu. Click it and a menu similar to the following should drop down -

The item "From" is at the top of that menu. Select it, and that item should then change to reflect that choice.

Enter the 'from' address for Runner's World in the text box after the item "contains".

Many of the other items in that screen are also pulldown menus, such as the one to choose the target mailbox destination. Clicking it should present you with a dropdown menu displaying all available mailboxes. Select the one you want as the recipient of thse emails.