Insert the pendrive into your computer
Back up any important data from the pendrive
Download the ISO file of the operating system or tool you want to install
Download and open a bootable USB creation tool
Select the pendrive in the tool
Select the ISO file in the tool
Choose the correct partition scheme and target system if required
Start the creation process
Wait until the process is complete
Safely eject the pendrive
Use the pendrive to boot the target computer from the BIOS or boot menu