Welcome to the Support Communities!
I'm assuming you are asking about the Mail application on your Macbook Pro?
The folders you are referring to are actually called Mailboxes.
The video tutorial below will give you a quick overview of how to organize your messages
Additional information can be found in the Mail application itself.
On the Menu Bar at the top of the window, click on Help > Mail Help
You can create mailboxes to organize messages. For example, if you receive messages from friends in a book club, you could create a mailbox to store all the messages related to the book club. You could organize your messages further by creating another mailbox inside the book club mailbox for each author you read.
You can create a mailbox within another mailbox, called a “subfolder.”
If you create a mailbox and a subfolder in one step, for example by typing “swim club/youth” in the Name field of the New Mailbox dialog, the top-level mailbox (in this example “swim club”) appears white and can’t be used to store messages. The subfolder (in this example “youth”) appears blue and can be used to store messages.
Some organizations may set up mailboxes in your account that are read-only. For example, a public folder may be used to provide information for all users of the mail system. You can’t create mailboxes within or save messages to these read-only mailboxes. To find out how to post messages to the mailbox, ask your mail administrator.
To reorder the mailboxes for an account in the Mail sidebar, simply drag a mailbox to a new location within the account.
I hope this information helps ....
Have a great day!