I am new to networking. I have some confusions regarding CBR and FTP? Are they any protocols like TCP or UDP or something else? When do we use them?
They are unrelated to each other.
FTP is an application (and protocol) used for file transfer. It uses TCP for transport, but FTP is considered an application protocol.
CBR is a quality of service term usually used in the context of codecs, describing how they convert analog signals to digital (and vice versa). It's not a term commonly used in the TCP/IP suite.
Constant Bit rate is not a protocol, but a description for an ideal situation.
FTP is a protocol, but it is above OSI layer-4 (transport layer), and it uses the transport layer to do its work. Questions about protocols above layer-4 are specifically off-topic.
TCP and UDP are layer-4 protocols. UDP is a best-effort, fire-and-forget transport protocol. TCP guarantees delivery.
Both CBR and FTP are traffic generators not traffic agents. Traffic agents are like UDP and TCP. Their main difference is as they said: FTP uses TCP for transferring packet and CBR uses UDP for transferring packet. And Note that: As its known the request through TCP has an Ack while the one through UDP has no ACK and in Network simulation the same scenario works if you are familiar with it.