Well that is a pretty general question Steven,
it would depend on what you want to do with the files etc... Some of the basics consist of (I am assuming you never opened a file before from a program)...
$fp = fopen("somefile",w+);
this opens the file and allows us to read and write to a file using the variable $fp as a pointer or address to the file.
Once open we can do operations such as read the file line by line:
while (!feof($fp)) {
$data =. fgets(fp,1024);
}// end while
this would get the lines in a file 1024 characters long or until the \n character was reached... the loop would end when loop reached the EOF marker of a file. (End of FIle)...
There are numerous other functions that you can look att: see
http://www.php.net/manual/en/ref.filesystem.php
as for tutorials to help you edit files try:
http://www.devshed.com/Server_Side/PHP/PHP101_5/
This should help you get started in file editing.... please come back with specific questions next time.
