Prior to High Sierra there was a Finder sidebar item called All My Files. This showed you a big list of all of your documents. This was replaced with the Recents list, which only shows documents you have opened and leaves out files you have created or downloaded, but haven't opened yet. You can easily re-create the All My Files list by making a Smart Folder and adding it to the Finder sidebar. You can customize this Smart Folder to better fit your needs.
The new Gallery View in Mojave allows you to see file data for the file selected. You can choose to show more or less of this data. You can also customize this data to pick which items are shown by default. This function isn't for the Gallery View only, however, as you can also see it in all four Finder views.
A new feature in macOS Mojave is the ability to edit and manipulate files directly in the Finder using Quick Actions. You can rotate and mark up images, mark up PDFs, trim video and audio, and even convert images to PDF files. In the future you will be able to do more with third-party extensions. You can currently build your own Quick Actions in Automator too.
A new feature in macOS Mojave is the ability to temporarily group files on your Desktop into Stacks. These Stacks can contain files of a similar kind, or groups organized by date or tags. You can expand and collapse any Stack to see what is inside, and use the file icons inside the Stack like regular icons. Desktop Stacks can help if your Desktop gets messy and you need to find files right now, but don't have time to organize your Desktop files at the moment.
The new Gallery View replaces Cover Flow View in macOS Mojave. It is useful for flipping though a folder full of images, PDFs or other document types when you need to find one using a large preview image. There are some customization options for Gallery View.
Quick Look gives you the ability to view the contents of files without needing to open them up in an app. You can easily view a single photo or document by pressing the spacebar. You can also page through PDF files or view groups of photos. If you open up the Quick Look window you can continue to select different files with the cursor or arrow keys and the window will reflect whatever is selected.
When you look in List View in the Finder, you'll see a file size for every file, but no size listed for any folders. You can still view the total size of a folder using one of several methods. You can Get Info on a folder to see the size and number of files. You can also use the File Inspector. Quick Look also displays the folder size. If you want to see the sizes of all folders in List View, you can enable that by changing a setting.
Instead of placing every file in a specific folder, you can tag your files for greater flexibility. Files can have more than one tag, so you can include a file with more than one project, task or collection. You can rename and assign colors to tags. You can easily view all of the files that have a tag, search for files by tag, or even create smart folders for a single tag or set of tags.
The way the Trash works is pretty straight-forward for your internal drive. But how about files on external or removable drives? Any file you put in the trash remains on that drive, but appears as a aggregated list when you view the Trash folder. You can only see files in the Trash on the same computer and user that threw them away.
Instead of dragging and dropping files to move them in the Finder, you can simply use Copy and Paste. This will create a copy of the file in the new location. But if you hold down the option key, this moves the file instead. This is similar to cutting and pasting files in other operating systems. You can copy and paste multiple files.
Tags are useful for many things. One idea is to use them to flag files to gather them together for a single use without moving the files from the folders where they reside. For instance, you may want to gather together files to send to someone or save a copy to an archive.
Creating a custom Finder icon for a file or folder is as simple as copy and paste. However, a common problem people experience is when they try to copy and paste a whole file as the new icon and get a generic image icon instead of the picture. The trick is to copy the image inside the file, and not the file itself.
You can rename multiple files easily in macOS High Sierra and other recent versions of macOS. The option to do so only appears when you have selected multiple files. You can choose to simply replace text in all filenames. Yo can also add text to the beginning or end of a filename. You can also set up formatted names, such as numbering groups of files.
In Icon View in the Finder, you have several options that are not available in list or column view. You can change the label size and move it to the right side. You can turn on an option to show additional information like image dimensions and how many files are contained in a folder. You can even set the background color of the Finder window to something other than white, or use an image as the background. Many of the same view options are available for the Desktop as well.
You can use folders to organize your files inside the Documents folder on your Mac. It is easy to create new folders. You can put folders inside of folders and use as many as you need to group your files however you want them. You can also easily move, rename and delete folders.
You can resize a window in the Finder and almost any app by clicking and dragging on the edges or corners of a window. You can use the Option key to drag opposite sides or all sides at once. The sides of a window will stop at the edges of the screen. You can also double-click a corner or edge to move that side to the edge of the screen or fill the entire screen without going into full screen mode.
An alternative to using Spotlight or the Finder to search for files is to use the Find command in the Terminal. You can search for files by name and refund the search by location, time and other factors. While not useful for everyday file searches, this could be used to search through large libraries of files for particular results.
New Mac users sometimes struggle learning how to renamed files and folders. You can rename items in the Finder simply by selecting the file and pressing Return to select the name, then typing to replace it. You can also rename files while you are working on them by clicking on the title bar of the window, or using File, Rename.
Although it has been around for many versions of macOS, the Arrange By setting in the Finder continues to confuse users who try to use it to set the sort order in a Finder window. Arrange By is for grouping files by kind, date, size and other criteria. For simple file name sorting, you should have it set to None, and then use the column headings to sort.
Power users love the Go To Folder command in the Finder. It allows you to type the path to a folder instead of using mouse clicks to navigate. You can use autocompletion to do this quickly, even if your folders have long names. The Go To Folder command can also be used in application open and save dialogs.