Making a directory: mkdir command. mkdir takes one or more filenames as options. Enter info mkdir or mkdir --help for more information.
Removing a directory: rmdir command. rmdir also takes one or more filenames as arguments. The directory must be empty before you can remove it.
cp sourcefile destinationfile
The -r (recursive) option is useful when copying directory content.
Renaming and moving files: mv command, e.g. mv file anotherfile. Both filenames may be either plain names, relative or absolute pathnames, just like the cp command uses.
Removing files: rmfile. Note that the -f option (force), e.g. for removing directories that are not empty, is very powerful, but be absolutely sure when you use it: there's no trashcan or recycle bin in the Unix command line, so when a file is gone, it is really gone.
The cp, mv and rm can be used interactively with the -i option. Since it offers a second chance to think about what you are about to do, aliassing these commands to their interactive counterparts may be a good thing for beginning users.
Comparing files: use the diff file1 file2 command. The diff command has about 40 options, read at least the help info (--help option).
Some systems offer ediff, a "diff to English" translator. The example below demonstrates that this might be a useful tool when comparing real life files:
tille:~>diff test1 test2 1,3c1,4 < This is some text from file1. < This is some more text from file1. < This is the same text in each file. --- > This is some text from file2. > This is some more text from file2. > This is the same text in each file. > This is text that only occurs in file2.
Read at least the built-in short help for these commands.