Yes, you have to sideload books from your computer to the 350 via USB cable because it does not have wireless capability. Unfortunately, the 350 does not work with B&N EPUB's or Apple iBooks. They both use a special type of Adobe DRM encryption. However, it does work with loads of other sources for EPUB's. There is a sticky thread at the top of the Sony forum about where to find books.
Sony has their own ebookstore which has most of what I need. You can browse their bookstore at the link below. You just can't purchase their books direct through your web browser. You have to use Sony's Reader Library software to purchase their books (very similar concept to how you purchase Apple's music through their iTunes software).
http://ebookstore.sony.com/
Some of my other favorite sources are Kobo, Borders, booksonboard.com and ebooks.com. There are also loads of sources for free public domain books like feedbooks.com, manybooks.net, gutenberg.org and even here on MobileRead. Smashwords is a popular source for indie authors.
Hope that helps!