If it were possible to use the same USB stick with another operating system, for example to store files to use on Windows, a virus in the other operating system could corrupt your Tails.
To store files in your Tails USB stick, use the [[Persistent Storage|doc/persistent_storage]]. To exchange files between Tails and another operating system, use a separate USB stick.
This is not possible using the recommended installation methods. Tails is designed to be a live system running from a removable media: USB stick or DVD.
No. Those installation methods are unsupported. They might not work at all, or worse: they might seem to work, but produce a USB stick that does *not* behave like Tails should. Follow the [[download and installation documentation|install]] instead.
If installed onto a USB stick, then it would be impossible to verify that the Tails on the USB stick is genuine. Trusting that a Tails USB stick is genuine should be based either on cryptographic verification or on personal trust (if you know someone you trust who can clone a Tails USB stick for you). But once Tails is installed on a USB stick it is not possible to use our cryptographic verification techniques anymore. Being able to trust your Tails USB stick is something that we really care about.
It is impossible to verify the integrity of a Tails USB stick or DVD while running Tails from it. It would be like asking to someone whether they are lying: a true liar would always pretend to tell the truth.
If you worry that your Tails might be corrupted, do a [[manual upgrade|upgrade]] from a trusted operating system to upgrade it to a trusted version of Tails.