take an image of server

You need to create device on NAS, add it to NW, label it and associate backup with that device (via pool/groups for example). I would not call it image backup as that is regular NW backup.  You mentioned NW7 in tags so with that version, that would be how you do it.  With that said, I see no reason why such backup would go to different place than others do.  If you are looking for image backup, then with NW7 product like HomeBase would be handy (but usually you would have some sort baseline procedure along with puppet server to keep configuration up to date and distributed along the landscape).

I think what you want is some kind of bare metal restore - that's not going to happen with NW7 out of the box.  You will need to install server B.  Then on server B you run restore of the backup of the server A and before you reboot it, make sure to adjust config files to reflect name and IP of server B (unless you know what you want and wish to exclude those from restore in the first place).

Creating device on NAS is explained in administration guide - you have share, within share create folder and create NSR device to use it.

yes my NetWorker version is 7.6.3.3.Build.870, and i have 7 client licenses free.

by creating device on NAS, you mean a directory right?

what i need to do is create an image of the server and restore it on a different server which will have a different configuration but yes the storage space that the original server had.