A pathname is a complete specification for a file with all its directories. A relative pathname is based on the current working directory. In Unix, upper case and lower case letters are not equivalent. You must type commands in the correct case. Almost all Unix commands are in lowercase.
Many commands have optional flags .
Some commands require a parameter, such as the name of a file. If a file name without a path is specified on a command, the file is assumed to be in the current directory. You always can specify the complete path for the file. When a file name is used on command, you usually can use wild cards to specify a group of commands. These commands manipulate directories and require the name of a directory as a parameter.