Summarize the following:
Go to https://www.icloud.com/ in your browser. You cannot upload files to iCloud from from the iPhone or iPad app. If you aren't signed into iCloud, enter your Apple ID email address and password and click before proceeding. It's a cloud-shaped icon near the top of the page. This cloud-shaped icon with an upward-facing arrow in it is near the top of the window. Click a photo that you want to upload. If you want to upload multiple photos at once, hold down the Ctrl (Windows) or Command (Mac) key while clicking each photo that you want to upload. It's in the bottom-right corner of the window. Doing so will immediately prompt the photo to upload to your iCloud Drive folder.
Open the iCloud website. Click iCloud Drive. Click the "Upload" button. Select a photo. Click Open.