Included in the Microsoft Office 2016 package is OneNote 2016, a tool to organise notes and thoughts. If you do not use OneNote 2016; it will still automatically start up the next time you boot your Windows device.
To prevent OneNote 2016 from starting up the Send to OneNote Tool, you can disable this behaviour.
To only hide the icon in the system tray: open OneNote and go to File > Options. Next, on the right hand side, click on Display and untick the box next to ‘Place OneNote icon in the notification area of the taskbar’. This should hide the icon in the tray.
Hiding the icon may be sufficient for you, however, the tool still starts every time you boot up your computer. Fully disabling the startup of the tool is done through the task manager. Open it (CTRL + Shift + ESC, or right click on your taskbar and choose Task Manager) and go to the Startup tab. There, disable the Send to OneNote Tool in the list of items. While you are at that screen, I suggest you also disable various other applications or services that may delay the startup of your computer.
OneNote will still function properly as it did before, but it will not automatically place an icon in your system tray or startup every time you boot up your computer.