So I have created a Squidoo account and will now be creating my first lens, but I am confused about what kind of content to add to it. I will be promoting a post from my blog, but I don't know if I should add all of the content of the post or just a short summary. And if I add just a summary, is it OK to add a link to the post at the very bottom saying something like "click here to continue reading"?
You're going to need much more content for a good lens then that. It should be about your entire niche or your entire blog, with loads of content and a handful of ways to get back to your site.
Content = King. It is always better to post unique content on squidoo. If you copy from a source then you must cite it. I think unique is better anyways