CurrentlySober

Let's say I have downloaded the Ubuntu 18.04.2 LTS ISO and I've imaged it to a usb drive, which is bootable.

I insert it in a laptop with windows on it, and it asks me if I wanna run it from the stick, or install it...

Well I totally understand the running from the stick part, but my question is that if I install it, does it wipe out / install over my Windows install, and from then on that's all there is on the laptop, or does it like give me an icon on the desktop that I click to run it like a normal program?

In essence, am I overwriting my win install, or just having an extra OS that I can turn on / turn off at will?

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