Why aren't my app icons showing up after installed? I have Moto X Style phone having Android 6.0.

Today I installed "Stereo Bluetooth Headset SBH52" app on my phone, but I am not able to open this app because there is no app launcher icon in the launcher. In Play Store, it's also showing Uninstall button only. I am able to see the app in Setting > Apps. Here, only Uninstall button is enabled.

I have one more app "Exchange Server" which is there in Apps list, but the icon is not available in the launcher.

I also have restarted the phone. I removed the SD card, then again installed these app from Play Store, but still the issue is there.

Why are there no app icons showing up?
Not all apps have explicit launchers (or app icon).
Take an example from Stereo Bluetooth Headset SBH52 app:

This application will not be visible in your phone's home screen. Access application settings via Smart Connect (LiveWare™ Manager), or via your phone's status bar.
(Emphasis added)

As for Exchange Server (or Exchange Services on Nexus stock ROM), it's only a back-end service used for communicating with Exchange server, with stock E-Mail app as its front-end UI.
Another example is Google PDF Viewer, where it's only prompted when opening a PDF file. (see How to open Google PDF Viewer app?).
If you want to force open the app, you might be interested in List all activities of an app.