Welcome to the light.
You’ll find that the Linux and FOSS communities are great and helpful.
You can start with this thread:
Arch is a more advanced user base and typically “upity” about helping newcomers so I would avoid most anything on that side. Sticking with Debian based or any of the many flavors of Ubuntus would be a good place to start.
Rufus, Balena Etcher are the most prominent ones for writing the ISO files to a USB to make it a bootable thumb drive.
First, if you have a model of the intended recipient, that would help us to help you start in the right direction choosing a compatible distro.
If it is “old” it could be that it may not support 64bit and we would have to run down a list of 32bit distros, there are still plenty out there. They may not be useful for video editing etc, but they would be fine for basic internet, video watching, mail…