The radio stac has several features.
Typically, on top is the audio panel.  This selects the radio(s)
to which you will be listening (monitoring).  There usually
are 2 communication radios (Com), 2 Navigational radios
(Nav), 1 Automatic Direction Finder (ADF), 1 Distance
Measuring Equipment (DME), and 1 Marker Beacon (MKR).
When you select one or more of these radios, you will hear
what is being broadcast, if anything, on the frequency shown
on the corresponding radio.  If you select the Comm radios,
you will be in contact with Air Traffic Control (ATC), and based
upon the frequency used, will be able to hear radio traffic.  If
you select the Nav, ADF or DME, you will receive the morse
code identifier for that particular station if you are within 50
miles of it or so.  If you select the Marker beacon, then you
will get a beeping sound as you pass over the outer,
middle and inner marker of an approach path.

Each of the Comm, Nav, ADF and DME have a window and
a knob which can be used to tune selected frequencies.
As I mentioned above, the Comm radios are for ATC.  Most
folks use Comm-1 for most of the ATC traffic.  The Nav
radios are for the various VOR/VOR-DME/VORTAC/ILS
stations.  Nav-1 refers to VOR-1, usually the upper one
right next to the altimeter (in a Cessna single).  This one
also has the glide slope for the ILS (Instrument Landing
System)

One thing I've done is to get a sectional chart for the
local area I wish to fly in and most of the frequencies
are there for the VOR's and such.

I hope this helps.