See on the main menu where it says 'System Editor'? Select that.
The system editor window opens up. Select the system you want to edit. A 'System', as defined by Uniden with these scanners, is any arbitrary collection of frequencies that generally make up a common radio system you want to scan. You can create a 'System' with just 1 or 2 conventional frequencies, or a System that is made up of dozens of frequencies in a trunked radio system and hundreds of talkgroups.
Your local police department's trunked radio system might be a system, with all their talkgroups organized neatly for alpha display on your scanner. Or your state might have an entire radio system used by all the county sheriffs, local police, EMS, fire, etc. and all that might be organized as a single huge system. Or, you might just have created a new System of conventional frequencies for maybe local police/fire/EMS/public works departments.
So anyway...
When you select the System editor from the main UASD menu, the system editor menu comes up, and you'll see a list of current Systems stored on your computer. Select one of them, and the editor for that particular system comes up.
If the system you selected to edit is a conventional one, then under Group Settings, you will see the alpha descriptors and the frequencies.
If the system you selected to edit is an LTR trunked system, then the frequencies for that radio system are on the first edit page. If it is a Motorola system, then look under 'Site settings' for the place to enter frequencies and other characteristics of that particular system. It really DOES make good sense for all this.
Once you get all your radio systems created and edited to your liking, you still need to put the information on your scanner from your computer. Select Configuration Editor from the main menu. Select the relevant configuration file. When the editor comes up, select the Systems tab.
The window on the left represents the Systems to be stored on your Scanner. The window on the right represents all the systems in your computer's database. Move systems from right to left as needed.
Now choose 'Write to Scanner', make sure your serial connection works, and you'll be presented with a window for writing the new Systems to your scanner.
Your list of Systems in your computer database should be closely guarded. Mine is well manicured and I water it daily. I'm always tweaking frequencies, talk groups, alpha descriptors, etc.
Just remember that the 'BANK' paradigm isn't really relevant with your 396. Like a computer, there's a central pool of memory and you're free to use it up as your see fit. But I guess a "System" is roughly equivalent to a 'BANK' on older scanners, except that a System can be just about any size, and it is further organized into groups and channels.
I hope that helps.