It depends on how complicated you want to get. If you want to have it just parse commands run them and pipe stuff, there are two things you need to do.
First, parse the command line input in a loop. Then use some of the string functions to parse the input. Here
is some info on string functions
Then you need to pipe data, open close files and run exec system calls. The basic idea is, that if you have a command, you first fork a new process (fork()), then execute that processs (exec() or a like syscall). If necessary you overwrite the stdin and stdout with either a pipe or output file. You may want to look at this fuctions/syscalls:
execl() (there are a lot more, type man exec)'
dup2() -- copies a file descriptor (this allows you to overwrite stdin or out with a pipe or file)
you can type man to look these up or do some searches on google. also, may favorite quick and easy c tutorial is