Power off the Xplained board and connect a network cable from the board into your router (a wireless adapter should also work just as easily, I'm going to use a cable for simplicities sake. Once your happy and problem free using a cable then moving onto a wireless adapter should be straight forward).
Once connected power up the board, either with external power (remember 5v max) or with the USB cable provided.
When the LED starts flashing in it's uniform heartbeat pattern, the onboard operating system is booted up. Give it a few more seconds to register itself on the network then its time to find it.
If your like me and can log onto your router through your host computer then it should be easy enough to find the network address of the board, if not then you will need to scan your network:
Im using ubuntu and will be using the nmap tool to scan my network. If you dont have it then you will need to install it:
sudo apt-get install nmap
then get the network range:
type "ifconfig" into your terminal and you should get something looking like:
eth0 | Link encap:Ethernet HWaddr 00:19:21:4b:c4:f2 |
| inet addr:192.168.1.70 Bcast:192.168.1.255 Mask:255.255.255.0 | |
| inet6 addr: fe80::219:21ff:fe4b:c4f2/64 Scope:Link | |
| UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1 | |
| RX packets:80294 errors:0 dropped:0 overruns:0 frame:0 | |
| TX packets:67087 errors:0 dropped:0 overruns:0 carrier:0 | |
| collisions:0 txqueuelen:1000 | |
| RX bytes:84059373 (84.0 MB) TX bytes:11129581 (11.1 MB) | |
| Interrupt:16 |
the line in bold is the important one, this tells us our network range can be anywhere between 192.168.1.0 and 192.168.1.255. Yours might be different so remember to use the address that you have when we continue below (in most cases it should be the same though).
We need to scan that range, so:
type "nmap -sP 192.168.1.0/24" remembering to use your ip range(you also might need to use it as sudo). and we should see something like:
Starting Nmap 6.40 ( http://nmap.org ) at 2014-10-04 17:39 BST
Nmap scan report for udhcp-1-21-1-62-5d-a5-41-75-38.home (192.168.1.96)
Host is up (0.00014s latency).
MAC Address: 62:5D:A5:41:75:38 (Unknown)
Nmap scan report for BThomehub.home (192.168.1.254)
Host is up (0.00086s latency).
MAC Address: CC:33:BB:49:47:12 (Sagemcom SAS)
Nmap scan report for personal-2aa894.home (192.168.1.70)
Host is up.
Nmap done: 256 IP addresses (3 hosts up) scanned in 7.64 seconds
This tells us that there are 3 devices present on the network, the first one highlighted in bold is the xplained board. The numbers in the brackets is the ip address of the board, this is what we need to ssh into it. for consistency, the other 2 devices on my network is my homehub(the router itself) and my host computer that we already knew about. Any other devices connected to your network will also be listed but we re only interested in the xplained board right now.
Once we have the ipaddress of the xplained board, currently 192.168.1.96 then we can ssh into it:
type "ssh 192.168.1.96 -l root" into a terminal, remembering to use the ip address you have obtained from your xplained board. the -l root says we want to logon as user:root which is the default user.
your command prompt should now read:
root@sama5d3_xplained:~#
This is a direct access to the xplained board, anything you type into that terminal will now be executed on the xplained board. to exit simply type"exit" and you will be logged off and return to your normal command prompt.
------------------------------------------------------------------------------------------------
This part may give you the same access as you would get connecting purely through the usb cable and accessing it with something like minicom on /dev/ttyACM0 but in a more native linuxy way. I'm more used to connecting with ssh so it's better for my "comfort zone!!".
******************************************DANGER*******************************************************
Don't assume the IP address of the xplained board will always be the same, it seems to change ip addresses everytime it logs onto the network, usually incrementing by 1. I've got a fix on my todo list but for now, this is better than anything, or for me at least 
******************************************BONUS*******************************************************
Use SCP to transfer a file from your host computer onto the xplained board through your network connection.
You need to know your xplained boards ip address plus the name and location of a file you want to copy.
make sure your terminal is at it's normal command prompt and not logged into the xplained board via ssh.
then:
scp /my_file_location/myfile root@192.168.1.96:~/
Your file will now be copied into the root home directory on the xplained board. it's possible to transfer to other directories and also change the filename aswell, the above is just a basic outline of how to go about transferring files.