I wish to make css manager for my website like wordpress's css manager. I wish to open css file in textarea in order to edit it than after pressing submit button, alterations in css file ought to be saved. Help me. Sorry for my bad british.

You need to learn PHP's filesystem functions (fopen , fwrite etc. )

But when your real question is emergency , essentially you can aquire a file's quite happy with :

file_get_contents("file.css");

and you can put new content to file for with :

file_put_contents("file.css");