We recommend Netscape Communicator for electronic mail. You probably need to do basic tasks like listing out your files, editing files, and changing permissions on files. A shell is a program that interprets your commands and runs the appropriate programs. UNIX in general is case sensitive. Upper and lower case letters are considered to be different.
Commands usually are all lower case.
If you type the man command as Man you will be told the command was not found. Filenames like foo and Foo are different names because f and F are different. Emacs is a better text editor that is recommended for writing longer text and program code. There are entire books about Emacs. Pine is an easy to learn mail program that handles MIME attachments.