In order to use CasparCG Server, you will need a client to control it.
CasparCG Server can be controlled by the ACMP protocol, which is a simple text-based TCP protocol.
See the wiki http://casparcg.com/wiki/CasparCG_2.0_AMCP_Protocol
for further description.
So the simplest client software for CasparCG Server is a TCP connection with telnet or putty or any other TCP console software.
But using a command based client is complicated and not user friendly, so there a some good client programs out there.
In this topic, a growing list of known CasparCG clients will be hold for you.