Um... RTFM?
Seriously though, what database are you using?
Do you mean you want to use a txt file INSTEAD of a database?
Theres no such thing as a 'database folder', but yes, sometimes databases are stored INSIDE folders.
You don't use txt files to host databases...
You never POST information to a database, you post to scripts, which put database in databases.
You don't open up databases, you connect to them, and it depends on what database you are using.
www.php.net
Start reading :-)