When you do not have an USB key to boot a PC to install an OS for example, know that through the DriveDroid application, your Androphone can replace your external storage device.
DriveDroid can transform your smartphone into an external storage device. By storing a disk image in .ISO or .IMG format on it, you will be able to boot your PC with the installation of an OS (like Linux). Obviously, this implies some preliminary steps. First you need to download the disk image to install on your PC (eg from the app, which has a download manager to access some free distributions). Then you need root your Android device because DriveDroid only works with devices that allow access to superuser rights. You understood it well, this app is for the lovers of experts hacks.