1. Select photos for your webpage. Press "Hold" to the right of the Photo Tray when selecting photos from different folders.
2. Click "Folder" at the top of the page and select "Export as HTML Page."
3. Choose your photo size, page title, and location to save the HTML page to.
4. Click "Next."
5. Choose a template for your photos and click "Finish."
Picasa will create an HTML webpage with the photos you selected in the template you chose. By default, these files will be saved in the "Picasa HTML Exports" folder inside "My Documents."
The last step is to put your files online. When you're ready, you'll want to upload all the new files from "My Documents\Picasa HTML Exports\Webpage Name" to the host's file manager or web directory.