You can create additional folders into which you can save e-mails, Click on the "+" sign to right of "FOLDER" under "TRASH" on the left hand side column. It will ask you what you want to name the new Folder. Type in whatever you want, eg Friends, Work etc. I think you then need to click "OK" to confirm the new Folder name. The new named Folder will appear under the title "Folder". Create as many Folders as you require, they appear alphabetically. Click on the mail you wish to save, then click on the icon to the right of "Spam". A list of the Folders you have created will appear as a list under icon, click on the Folder name where you wish to save that e-mail. You can also "drag and drop" e-mails to the appropriate Folder. Hope I have described that adequately and that it works!
If you do not wish to see the list of Folders in the left hand column, click on the downward pointing arrow to the left of "Folders" in the left hand column, click the right pointing arrow to show them.