Powerline Networking -- Diff between Bridge and Adapter

I’m trying to set up a powerline network in my home. I have a desktop (which has the DSL setup on it) and a notebook (both of which are PCs). In a few months or so I’ll also have a Mac notebook that I will want to connect to the network, but this is not of big importance to me at the current time.

I have a Netgear XA601 Powerline USB Adapter. The booklet tells me that I need a router (which I understand. I may get the RP614 or the MR814 for wireless possibilities – if you have an opinion of one over the other that would help. I heard that the RP614 may be faster (?).). It also says that I should get the XE602 Adapter (which I believe is the same as my XA601 but uses ethernet cord instead of the USB). However, when I called customer service they told me that I should get two XE102 Powerline Bridges instead of the XE602 Adapter.

What’s the difference between an Adapter and a Bridge? Why do I have to get two Bridges, but only need one Adapter?

I’m new to networking and am having a heck of a time trying to figure out just what I need without a trial and error test.