You need to learn the basics then. These are different login shells which will be executed at the time of user logs in. Each shells has its own capablities and features. It will be specified in /etc/passwd file.
Basic definition of shell:
Users of the UNIX system don't have a direct interaction with the kernel. Instead, the user always works with a program called the UNIX shell. A shell can be considered a command interpreter. The shell takes user commands, interprets them, and takes the necessary action to execute them. It also provides the output of these commands to the user.
C shell: It uses a C language-like syntax for shell programming.
Korn shell: It has more complex and advanced features than the Bourne or C shell and takes more time to master
