How to upload photos from Shotwell?

First, here are Shotwell's help pages for Publishing to the web , and for Exporting photos. You would be publishing images (and uploading over the Internet) if your target is a service like Facebook, or Picasa, or Flickr, something like that. You would be exporting images if your target is another folder or local drive or a USB key, for example. Since I'm unclear on exactly what you need I'll explain several options.

Exporting
If you just need to choose a set of images already in Shotwell, and you can bring them to class on a memory card or burned CD, or even use a network drive at the school, then use the Export function. Plus, if you are shooting RAW or some other format, and need to convert to JPEG before uploading, you are going to use the Export function first, even if you are uploading to a web service later. Exporting can both move files and convert image formats, so you may need both functionalities.

• Open Shotwell.
• Select one or more images.
• Shift + Ctrl + E to bring up the Export dialogue.
• Choose your export options, file format, size, etc.
• Now just pick a target and your photos are exported, done.

Publishing
Shotwell can currently Publish to the following online services: Facebook, Flickr, Picasa Web Albums, Piwigo, Tumblr, Yandex.Fotki, and YouTube. If your target isn't one of these your only option is to Export, explained above. If you are using one of these services follow the steps below.

• Open Shotwell.
• Select one or more images.
• Shift + Ctrl + P (or click the Publish button on the bottom toolbar) to bring up the Publish dialogue.
• From there, the steps vary slightly depending on the service. Follow the prompts to log-in with the target service, hopefully it is easy from that point on.

If you run in to problems just edit your question with which step you are stuck at, so we can edit the answer and make it better.

Other options
Also, if you want a really simple option you can just put the pictures for your homework assignment in your Ubuntu One folder at which point they are automatically uploaded to your Ubuntu One cloud folder (assuming you have configured the service). Dropbox is another good choice, with the added benefit of having a public photo gallery that you could use to show off the photos.