The safest way to prevent an app from launching at startup is to go through the app's settings and turn off the setting that tells the app to launch. This is best because you are using the app's own settings.
The next safest way is to open Task Manager and turn to the "Startup apps" tab. There you can disable an app from launching at startup. This is not as safe as the first method, because you are actually interfering with the app's normal functioning. However, you're using a Windows control, which will be conservative.
The riskiest method is to use a third-party app.