Move the contents of one file to another. The first ceases to exist and the second is created and contains the identical information as the original. The option -i asks if the file should be remove. For safety alias rm with rm -i in your .cshrc file cat Concatenate files. This may be a bit technical, but here goes.
Cat copies the standard input into the standard output.
In general it is used as above, to combine two files head to tail, but it can also be used to edit small files, by giving the cat command with only one filename. When finished hit control-D. mkdir Make a directory. This removes an empty directory. When used with no arguments, it puts you into the home directory, i.e., the one you were in when you first logged on. This puts you in the subdirectory named dirname.