Don't worry it's easy
If you try opening an unsigned app by double-clicking it, it won’t work. You’ll see an “[App Name] can’t be opened because it is from an unidentified developer” message.
Of course, there may be a time when you come upon an unsigned app that you need to use. If you trust the developer, you can tell your Mac to open it anyway.
Warning: Gatekeeper is a security feature, and it’s on by default for a reason. Only run apps you trust.
To open an unsigned app, you need to right-click or Control-click the app and select “Open”. This works on macOS Sierra as well as previous versions of macOS.
You’ll be warned that the app is from an unidentified developer–in other words, it isn’t signed with a valid developer signature. If you trust the app, click “Open” to run it.
That’s it. Your Mac will remember this setting for each specific app you allow to run, and you won’t be asked again the next time you run that app. You’ll just have to do this the first time you want to run a new unsigned app.
This is the best, most secure way to run a handful of unsigned apps. Just allow each specific app as you go, making sure you trust each app before you run it.