This is documentation for Mathematica 8, which was
based on an earlier version of the Wolfram Language.
View current documentation (Version 11.2)

Newlines and Tabs in Strings

\na newline (line feed) to be included in a string
\ta tab to be included in a string

Explicit representations of newlines and tabs in strings.

This prints on two lines.
In[1]:=
Click for copyable input
Out[1]=
In InputForm there is an explicit to represent the newline.
In[2]:=
Click for copyable input
Out[2]//InputForm=
Mathematica keeps line breaks entered within a string.
In[3]:=
Click for copyable input
Out[3]=
There is a newline in the string.
In[4]:=
Click for copyable input
Out[4]//InputForm=
With a single backslash at the end of a line, Mathematica ignores the line break.
In[5]:=
Click for copyable input
Out[5]=
You should realize that even though it is possible to achieve some formatting of Mathematica output by creating strings which contain raw tabs and newlines, this is rarely a good idea. Typically a much better approach is to use the higher-level Mathematica formatting primitives discussed in "String-Oriented Output Formats", "Output Formats for Numbers", and "Tables and Matrices". These primitives will always yield consistent output, independent of such issues as the positions of tab settings on a particular device.
In strings with newlines, text is always aligned on the left.
In[6]:=
Click for copyable input
Out[6]=
The front end formatting construct Column gives more control. Here text is aligned on the right.
In[7]:=
Click for copyable input
Out[7]=
And here the text is centered.
In[8]:=
Click for copyable input
Out[8]=