If you need to quickly see the hidden files when trying to open a file from an app, use the keyboard shortcut Command+Shift+period (AKA greater-than key). This reveals all hidden files and folders in the standard Open File dialog boxes in apps. Use it a second time to toggle this setting off.
Conditional Highlighting in Numbers lets you color a cell based on the contents of that cell. If you need to set a cell to highlight based on the contents of other cells, you can use the IF function first, and then the conditional highlighting based on the results of that IF function.
If you accidentally record video on your iPhone in vertical mode, you end up with two ugly black bars on either side of the video when viewing it on a TV. You can use iMovie to fill in those sides with an animated background, or a blurry copy of the same video. Take a look at a variety of techniques for dealing with vertical video in iMovie.