OK, first is this a USB stick (pen drive)? If so you are good there.
Does it have data on it? If it does, back it up, because the media creation tool is going to format it, make it bootable and copy the Windows 10 install files to it. So any data that is on it will be gone after the media creation tool is finished with it.
First step after running the tool is the Licensing Agreement, no choice here, you have to Accept Next it asks you if you wish to Upgrade this PC or Create installation media for another PC. Select the latter.
Now it asks you to select the version of Windows 10 installation media you want. It defaults to what it thinks you need for the PC you are building the media on. If the computer you are using to make...