\n in PHP (5.2.11)

I've ever stucked with \n. If we used ('') to convert string and put \n to the string then the \n will be appeared in html converted. So we gotta used ("") to put \n to make it disappered. That's all but it takes me 1 day to conclude this... haha... programming is better when we know the basic using. And it is the using of ("") and ('').

See the result of these code in browser:
echo "test \n";
echi 'test \n';