l am sorry if my questions are sometimes wage, l am totally new in this field.
l know com stands for Communication and Nav stands for Navigation. l wanna know exactly when l push comm.1 or comm.2 button what will happens? and the same for navigation.

By pushing comm button, l can listen only to the radio? which one connects me to the ground unit?

Depends on how ur audio panel is set up in the aircraft u r in.
Some allow u to listen to only one device at a time. Others offer a lot more versatility.
In my plane for example, there is a knob that will move between Com 1 & Com 2, the two Nav/Com radios installed in the panel. Switching between the two allows me to listen & talk on the selected radio. There r however buttons on the audio panel that will also allow me to additionally monitor the other Com radio from the one the knob has selected, or monitor either Nav frequency that is tuned on either radio or other receivers such as NDB, Marker Beacon, etc. In that manner u could for example be on with Approach or a Tower frequency on ur selected radio & still monitor the ATIS frequency, a VOR, the marker beacons, etc.

Sounds like u r describing the selector buttons on the audio panel. These select the source of audio signal for the speakers or headphones.

Do not know exactly what u mean by the ''ground unit.'' With a typical audio panel, u have a miniature toggle switch or a push on/push off button for each device. Push ''comm1'' to connect the audio output of the #1 comm radio to ur headphones or ''comm2'' to connect to the #2 comm radio.

The features of these audio panels vary; some include additional devices like Marker Beacon receivers.

If u need to understand more, ask ur instructor to explain the audio panel to you.

Good luck!

As other people have mentioned, audio panels vary. Typically, u will have two navigation radios & two communication radios. If u were always listening to every radio, you'd be constantly bombarded with junk. So the audio panel provides u a way to select what you're listening to & what you're talking to.

Starting with the communication radios, u usually have a primary selector & a monitor button for each radio. The primary selector allows u to listen to a radio & select which radio u would transmit on if u pushed the 'push to talk' button. This is probably ur most frequently used button. If you're using com1 to talk to ground control & have com2 set for the tower frequency, u would push the selector for com2 to switch to talking & listening on com2 instead of com1.

There is usually a monitor button that allows u to listen to a com radio without changing which one u talk on. You might be talking to air traffic control on com2 & have com1 set to the terminal information frequency for an airport u plan to land it. You might push the com1 monitor button for a few seconds to check if u r in range of the terminal information broadcast.

As for the navigation radios, u usually only need to listen to them in certain circumstances. Probably the most common is to identify a navigational aid. If u have, say, nav1 tuned to a VOR, u may want to make sure it is actually receiving that VOR & that the VOR is operational. The way to do this would be to push the nav1 monitor button & listen. The VOR will transmit an identification code (its identifier in morse code, also indicated as dots & dashes on approach plates, sectional charts, & the like). This allows u to confirm that u r strongly receiving the correct signal. You can not transmit on navigation radios, so there is only a monitor button.

Again, audio layouts & panel capabilities vary. However, the basic setup of two navigation radios, two communication radios, & a way to monitor any combination of them, is present on the majority of aircraft.