The shell environment has 2 variables which deal with the prompt the shell shows you: PS1 and PS2. The first prompt string (PS1) is the prompt you see from the shell for most interactions. It can contain literal strings, and also a great number of symbolic variables. These variables can include the time, your present working directory, the name of the machine you are logged into, ....
The second prompt string comes into play when you do not completely enter in a command line, and the shell is looking for you to enter more information. For example, if you escape the carriage return at the end of the line, the shell assumes you are still entering a command. This string is typically set to .