The Trade Platform blueprints cost 2,000 bytes to unlock, is produced in a medium printer and requires iron, tungsten and compound. This makes it quite a late game item as you will need to have visited at least two planets (Desolo & Novus are easiest) to collect the iron and tungsten.
You're then going to need some scrap to trade. Scrap can be found as cargo in some space ship wrecks on the surface of other planets but a much more reliable source is using your own shredder to process debris.
Once you've got your scrap and the trade platform interact with it to swap your scrap for something more useful. The rarer the material you want, the more scrap you'll need.
For more information about the Trade Platform visit the online gamepedia.
https://astroneer.gamepedia.com/Trade_Platform