It sounds silly, but one of the issues with Windows 8.1 is that the OS no longer pins newly installed apps on your Start screen. So you need to know where to find these apps, and then how to pin them to the Start screen—or, in the case of desktop apps, to your taskbar—so you can access them more easily going forward.
Why would Microsoft make such a change? The issue was that with the initial shipping version of Windows 8, legacy desktop applications could spew numerous tiles on the Start screen when installed; two notable examples are Office and Visual Studio. This wasn't an issue with Metro apps, which were only allowed to place one tile on the Start screen at install time.
Apparently, Microsoft decided to "fix" this issue by going in the exact opposite direction: Amazing, no tiles appear on the Start screen when you install a Metro or desktop app in Windows 8.1.
Of course, most people will expect to have installed apps be pinned for easy access from the Start screen (Metro and/or desktop) or taskbar (desktop apps only). Unfortunately, you need to do this yourself.
First, install an app. Any app. Desktop or Metro, doesn't matter. If it's a Metro app, you will of course see an app installed notification.
But it doesn't appear on the Start screen. So you must instead access the Apps view, which is found "below" the Start screen. To get there, swipe up from the bottom of the screen with a touch-based system. Or mouse down to the lower left corner of the Start screen and click the down arrow that appears.
The Apps view appears.
Apps you have recently installed have the text "NEW" next to their name. But actually finding a newly-installed app can be difficult if you have a lot of apps already installed, as I do.
A few tips for finding the app. You can use Search, up in the right corner of the Apps view, if you know the name, though it's worth noting that some apps use illogical names; Visual Studio Express for Windows Phone, for example, identifies itself as VS Express for Windows Phone for some reason. Or, you can sort the Apps view by Recently installed to put those apps right at the front of the list.
To pin the app to the Start screen or taskbar, select the app—mouse users can use a right-click—and then choose Pin to Start or Pin to Taskbar from the app bar that appears. (Remember: Metro apps can only be pinned to the Start screen.)
Voila. You're up and running.