You can connect to your EV3 from your PC using a command line interface.
On Linux or Unix system, you start a terminal and type
This creates a secure shell connection to the EV3. Press Enter when prompted for the password. The first time you connect, you will be asked to confirm the identity of the machine.
You should replace 10.0.1.1 by the IP address of your EV3, e.g. by the Wifi IP address. You can also use a name rather than an IP address if you put it in your /etc/hosts file.
On Windows, you need to install an ssh client to do this. A good one is putty: http://www.chiark.greenend.org.uk/~sgtatham/putty/.
You can also use scp to copy files to the EV3, or in Windows pscp from the same web site as putty.
You do not need to connect to your EV3 in this way, and if you do not know Linux, you can corrupt your SD card if you are not careful, as you have full root access to the Linux system on the EV3.
Some of the reasons for connecting to the EV3 in this way are: