Squarespace is everywhere these days. I hear their ads on Sirius XM. And tonight, I just saw their television ad on the Super Bowl.
I've hosted Sketchbook B on Squarespace since I started the blog in 2007. It's crazy to see how much they've grown and their product has gotten significantly better over time. I wrote a brief review of Squarespace 6 last year. They've added a bunch of features since that review.
If you've spent any time with a content management system like Wordpress, you should be able to figure out Squarespace quickly. It's pretty intuitive. But if you know some CSS, you'll be able to get even more out of it.
If you are the type of person that learns better from a book, Columbia designer Kris Black actually wrote the book on Squarespace. He's a illustrator, former Squarespace-tech-support employee and all-around good guy. His book, Squarespace 6 for Dummies, is available through Amazon, on Kindle and Apple's iBooks store. I have a copy of it and Kris really does a good job of summarizing the basics. So if you have decided to start a Squarespace site and want a good introductory book, pick it up.