Some operating systems distinguish one type of file from another. For example a database file is stored in a different way than an executable program. In order to be as simple and general as possible, UNIX makes no assumption about what is in a file, and so it says that any sequence of bytes is a file. The exact type of file that it is doesn't matter to UNIX, although the program that reads and interprets the file expects it to be a certain type. Files may be stored on long-term storage devices like hard or floppy disks, but they are organized in logical clusters called directories.
Every user has a directory called their home directory.
When you log in, you are placed in your home directory. Files have names so that we can tell UNIX to do things with them. Contrary to what you might have learned in other places, you can have numbers as file names, or you can use dashes or pluses, or asterisks or even blanks. Blanks, however, present a slight problem, since UNIX doesn't know where the file's name ends. The slash is the one forbidden character in file names, since it is used to separate directory names.