First thing, find the IP address of the box.
Next, open your browser on your computer and enter that IP address with hppt:// at the beginning as, for example, http://192.168.0.32 This will take you to the login page of the webUI of the NAS.
Read the section in the manual under 'Configuration' --> 'Web UI Login' because this is where you can setup the NAS just how you want it.
Login using your password if you have set one - if no password follow the instructions for setting one otherwise anyone can access your NAS and make changes which can lock you out. Also give the unit a fixed IP address on your lan.
Next check that the hard disks are setup as you want them. If they are move on to setting up users (one or more as necessary) and don't forget to give them a password..
Once you have user/users setup you can attach services to the user/users.
CIFS/SMB for viewing files and folders from a windows computer.
FTP for bulk file transfer (use FileZills FTP client on windows).
Once you have the basics setup you should be able to access the NAS using, for example, windows explorer (if you use windows) under network - the first access will ask for the user password (tick the 'remember password' unless you want to enter it every time).
Once you have access to 'Volume_1' and/or 'Volume_2' you can make any directories you want and have access to them.