Once you've finished your album and you're ready to export for the web, click the Export icon and choose Export for Web. The spreads are exported at 1,000 pixels high and the width is proportionate to the album size you've designed.
Once you click Export for Web, you'll be prompted to select an export folder location on your hard drive. Once you've done that, you'll be able to select your Export Options.
Pages: You can choose to export the entire range of pages in your album or you can select a range of pages to export individual spreads.
Color Profile: The color profile is locked at sRGB as this will be viewed on the web.
Export File Names: You can toggle this on to export your spreads with the filenames showing for each image in your spreads. This can be useful for proof books and client previews of your album.
Once you've selected your options, click the Export button to being the export process.