how to download videos and pictures from iphone6

You can copy them to a computer using the instructions in Import photos and videos from your iPhone, iPad, or iPod touch to your Mac or Windows PC - Apple Support

When you do a backup of the phone, either to iCloud or iTunes, photos and videos in the Camera Roll are included in the backup. Note that the backup is stored in a format meant only to be used in doing a full restore of the phone so you won't be able to view the contents of the backup. More information on how to back up: Back up and restore your iPhone, iPad, or iPod touch using iCloud or iTunes - Apple Support