Creating a folder is fairly simple. Just hover your mouse over the Listings tab and click on "Folders". Then click on the Create Folder button, and you will be taken to a page where you will enter the name of your folder, a description (optional) and a color.
After you save your folder, go back to the Saved Listings page and select the listings you want to put into the folder by checking the box next to them. Once they are selected, at the top of the page there's an option that says "Move selected item(s) to______" and a drop-down menu where you will choose the folder to put them in. Choose your new folder, and click the blue Move button.
In the future when you want to only show the listings you have in that particular folder, use the filter at the top to select the folder. Hope that helps!