What is 868? Does that just make it European standard?
The explorer generally takes care of voltages for you and breaks out the pins to make them more accessible.
The short answer is that you will not need anything extra to do UART - just use pin 2 for data out and pin 3 for data in. Read up on page 6 of the datasheet
and ask more specific questions afterwards.
Also, I'd recommend finding an Xbee tutorial to get you started - configuration is pretty easy once you know how to do it but can be tricky if you're new although I'm assuming you're using Series 2. If you're using Series 1, I've heard that it works pretty much out-of-box.