I have installed ubuntu on a 3 TB internal hard drive. I want to use it as a server. How do I share the entire internal hard drive on my network?
Create a Samba share with Nautilus
This is probably the easiest way.
The first time you do this, you will be asked if you want to install samba. Your password will be needed to do so. And on a more general note: This is very basic. Next time, try a google search.
There are other methods such as creating an FTP server or using ssh and sftp. I will be happy to go into details on those if you request it in a comment.