When this tutorial was written, there were 16 options for the 'ls' command. It is worth the effort to memorize this set and learn others as you need them. It is my guess that neither Thompson nor Ritchie could type because they made the basic commands very short and seldom used any vowels. The entire Unix system is case-sensitive. This means that LS, Ls, lS, and ls are all interpreted differently.
Most commands are lower case.
We'll alert you when upper case characters are needed for commands or options. For those of you just starting to use your account you may not yet have any regular files in your account. You will however have some dot files. These files and directories are the ones that you will work with most. As you work, you will save files to your account.