How do I open a file to write content to?
You need to create a filehandle, which is a pointer to a file, that you wish to write too.
Use the fopen function to open a file, and pass the name of the file as the first parameter and what you want to do with it second - in this case 'w' for write.
Then simple use fwrite to write to your file, and close it with fclose.
Here's a simple example that will create a file in the directory called example.txt and write to it with just a few lines of PHP code.
<?php
$myfile = fopen("example.txt","w");
fwrite($myfile,"That was easy!");
fclose($myfile);
?>
Congratulations, you have just written text to a file using PHP!
If you get an error message doing this on a web server, make sure you have the relevant permissions to write to the directory you are running the script in.