A comms console is used to trade with passing interstellar trader vessels or for communicating with other factions.
You will not receive any notifications about passing trade ships until it is built.
Select a colonist and right-click the comms console.
Ordering a colonist to use the console will bring up a menu showing the available factions, or trade ships.
When interacting with a faction with goodwill above -50, there is an option to give a goodwill gift for 300 silver. It will improve goodwill, by a value dependent on the colonist's Social skill and Talking and Hearing capabilities.
When interacting with a neutral faction (goodwill above 0), you can request trade caravans from them. Doing so will cost 600 silver (300 if colony goodwill is above 40), and brings up a menu asking which type of trade caravan is desired.
In addition, you can request immediate military aid from a faction with goodwill above 40. This costs 25 goodwill.