What's the difference between a UseCase and a Workflow?

I've always wondered what the difference between a Use Case and a work flow is, and how they relate to each other...

I ask, because I clearly see the way to develop a repository layer, and a Service layer above that, but the logic right above that layer quickly turns into, in my case, a set of webpages that seem to do a little of this and that...and I'm not sure how to describe them (what's a webpage that lists invoices as well as offers one click deleting of one or more of them? Is that a webpage that contains two use cases? or two workflows? Or the webpage is a workflow that contains two use cases? etc...)

As you can see, I'm pretty hazy on it all and would like to sort it out for once.

Thanks for your advice.