Common issues to address when setting it up:
Even the blank App Hello world can have issues
https://developer.android.com/sdk/index.html
I have downloaded new sdk's and didn't load them in the c:\program files folder and this sometimes fixed the buggy issues.
Try:
Build
Clean Project
Rebuild Project
Also:
File
Invalidate Caches / Restart...
Use the SDK manager to download updates
Rendering Problems:
https://www.youtube.com/watch?v=22pz5vnBEus
Gradle issues:
https://www.youtube.com/watch?v=22pz5vnBEus
Other issues can be from installing plugins. Android Studio will show you what is default and have the uninstall option for what isn't. Uninstall them and you may see the error disappear.