In the meantime here we go with the short tips version:
Antennas are split between Relays (only the dish antennas, you can check it in the OAB with shift pressed while hovering the part) and normal Antennas
Only Relays can be used to transfer signal between two vessels. Normal antennas can not forward, only receive signal from other relays (or KSC)
Signal may be blocked by a celestial body if the planet is between the vessel and the relay
Each Antenna has a range (indicated in meters / kilometers / etc. in the OAB). To communicate two vessels should be each one in the range of the other (you can use the Rulers in map view to check this)
Relays should be powered (EC > 0) to be functional. This can be disabled in Mods > Settings.
Stock CommNet has higher ranges, we are using the lower antenna ranges from KSP1. Even here, shift in the OAB to see the ranges
Connections are limited to antennas with the same Bands. This means you can create different networks. A vessel can connect to another only if both have the same Band. You can add multiple bands to a vessel using multiple antennas or using higher level antennas. (You can check this in the OAB with shift pressed in the "Signal Modulator" section)
In the meantime here we go with the short tips version: