Can I use a flash drive USB for extra storage
Sure, but understand flash drives were never intended as permanent storage devices. They were designed for things like taking home a document from work. Or taking a copy of a project to school.
Flash drives are fragile devices. You can "zap" them with static just by sliding them in and out of a pocket. They can easily be dropped and stepped on. Or easily lost or stolen.
"Expanding memory" is different than "extra storage". If you mean to improve your computer's performance by, in effect, adding more RAM, then you can do that with a flash drive using Windows "ReadyBoost" feature. That said, the same issues with fragility of these devices applies.
See
ReadyBoost in Windows 10.
However, in many cases, using ReadyBoost does not help performance because data transfers via USB are much slower than RAM. See
Is Windows ReadyBoost Worth Using?
It might be worth looking into upgrading your RAM instead of using ReadyBoost as permanent and better solution.