Moving a contact to Favorite folder
You can find your favorite/important user's email at the upper section of thread list and in the navigation bar there is a separate favorite folder where you can select a specific user as shown below.
To include certain messages to your Favorites list, select it from the sidebar and click on the Heart icon shown below.
To remove a message from your Favorites list, click on the message you have hearted and undo it.
Moving a Messages to Starred Folder
To move message into starred folder just click on message and select Star from menu. You can find your star message in starred folder . You can also swipe towards left and select more option to star a message.
To Unstar a message go to starred folder and click on message and select Unstar from menu shown below.
Rearrange your folders in the order that you like. Select the folder you want to move as shown below.
Drag and drop the folder in the position you want to move it.
On macOS, you can edit the Toolbar via Right Click / 2 finger tap on the Toolbar > tap on 'Customize Toolbar'. Then you can drag and drop the icons into the toolbar to customize it. You can also drag the default set into the Toolbar.