to "read a file" or "access a database" across the internet depends greatly on what
exactly you want to do. "Reading a file" can be very simple... in fact, that's what you're doing when you surf the web: your web browser reads certain kinds of files and displays them in a browser window.
Of course, that's not the only way to read files "across the internet." You can also Telnet or FTP, or you can communicate at lower levels for more specific, custom operations. Databases are the same way: how do you want to "access" a database? Using a web browser? Using Telnet? Using a socket? Many questions, Grasshopper. For us to place you upon the path to enlightenment you must better elucidate the task you would like to accomplish. The Most Powerful and All Knowing "Search" box at the top of the screen is probably your best place to start... just type in what you want to do and see if it hasn't already been covered in sufficient detail in other posts.