As you are going to be uploading to YouTube anyway you can use the YouTube Video Editor that they include for free in Creator Studio. It includes the ability to cut and spice videos as well as add music or other audio channels. YouTube also includes a selection of free (as in beer and speech to the degree that you can use it on YouTube) music that you can easily add to the background.
There are several video tutorials available on YouTube if you search for YouTube Video Editor Tutorial, such as this tutorial for 2017.
Outside of that the free ones I know of are mostly Linux based so will be of no use for a Windows 10 user.
For older versions of Windows and those of us living in the past there was Windows Movie Maker included as part of Windows Essentials (see a past answer for details). If you are using Windows 10 or living in a time post January 2017 then Movie Maker is no longer available.