If you're using Google Photos (rather than the Gallery app) your photos have already been uploaded to the web and stored in the cloud.
https://www.theedublogger.com/google-photos-guide/
If you want to use a different online storage facility, your first step should be to see if that facility has its own Android app. (If it has then, clearly, the easiest way to upload your images to that facility is probably to use their dedicated app).
Otherwise it's easiest to achieve your aims in a two-stage process, whereby you copy your images to a Windows desktop or laptop first and then transfer them to the cloud (or to a memory stick) from there.