You can temporarily <strong>turn your own computer into a secure machine</strong>. You can also <strong>stay safe while using the computer of somebody else</strong>.
You don't have to worry about the computer having viruses because Tails runs independently from the other operating system and never uses the hard disk.But, Tails cannot always protect you if you install it from a computer with viruses or if you use it on a computer with malicious hardware, like keyloggers.
On the contrary, Tails never writes anything to the hard disk and only runs from the memory of the computer. The memory is entirely deleted when you shutdown Tails, erasing all possible traces.
You can <strong>save some of your files and configuration</strong> in an encrypted Persistent Storage on the USB stick: your documents, your browser bookmarks, your emails, and even some additional software.