I purchased an SSD and I want to download Windows 10 on that. I want to download Windows 10 installer on my USB drive, however, that USB drive has some very important photos and I'm afraid that if I attempt to download Windows installer on it, all the photos and documents on the USB drive might get corrupted or something like that. Will this happen?
This is true whether you use the Windows 10 Media Creation Tool (MCT) or a utility such as Rufus to create a bootable USB drive.
Completely wiping it is part and parcel of the process and Rufus, like the MCT, warns you of this as well.
Either get another USB thumb drive (16GB ones are dirt cheap and 8GB ones even cheaper) or copy those pictures off on to an external backup drive before you use the USB thumb drive they're currently on.
Windows 10 Clean install tutorial This tutorial is intended to help you, step by step, to perform a clean install of Windows version 10, build 1709 or newer but can be equally applied to earlier installer versions which may simply lack some of the Cortana assisted settings screens but should...
You literally need to stop whatever it is you're doing right now and backup those files. You say you have very important photos on this USB drive, but if you have files that aren't properly backed up, the only question isn't whether or not you'll eventually you lose your files, but when. If these are truly important, a backup is the minimum level of responsible upkeep; you ideally want at least three copies in at least two different formats with at least one copy off-site.
however, that USB drive has some very important photos and I'm afraid that if I attempt to download Windows installer on it, all the photos and documents on the USB drive might get corrupted or something like that.