Its now built-in in Serial class in the Arduino framework. No need for additional library or function.
The usage will depend of the data type of your variables.
If they are int, it would be %d or %i :
Serial.printf("Var 1:%d\nVar 2:%d\nVar 3:%d\n", var1, var2, var3);
If they are string, it would be %s :
Serial.printf("Var 1:%s\nVar 2:%s\nVar 3:%s\n", var1, var2, var3);
More details about formatting tips on the printf format reference page : http://www.cplusplus.com/reference/cstdio/printf/
\n is the escape sequence for the line feed.
Escape sequences are used to represent certain special characters within string literals and character literals.