There are several ways of accessing Raspberry Pi files through network. One of preferred ways is to use Secure Copy (SCP). This is a file sending command allowing transferring files over SSH. This is secure way of sending files between Raspberry Pi boards or other Linux machines. In order to use with Windows you need special software like WinSCP.
So as you can see it requires additional software to access files from windows. But if you are used to transfer files via FTP, then you have another option – SFTP which is an FTP with encryption. SFTP is already enabled in Raspbian and can be used right away. Be sure that your FPT client supports sftp protocol. For instance FileZilla, Bitvise and same WinSCP clients work without problem. In order to connect to Raspberry Pi via sftp you need to enter IP address and port 22. Log in by using your connection credentials that are pi/raspberry by default. Once connected you can drag and drop your files in and out.
If you want to move a bit forward and be able to connect to sftp server from outside of your local network you may need to use port forwarding on port 22. More on port forwarding here.