how can i download all my photos and videos in one click

See→Transfer photos and videos from your iPhone, iPad, or iPod touch - Apple Support, which describes several methods.

By far the easiest way is with iCloud. Once you set it up it will automatically sync your photos to iCloud and any other devices that share the iCloud account, such as iPads, Macs, or PCs with the free iCloud for Windows app. And it will do it in real time; take a new photo, and it will be on all of the other devices within seconds.

Download where? From where?