Platinum is the currency that is purchased with real money and can buy things such as cosmetics, other Warframes and weapons etc. However, platinum can, in fact, be earned without having to put any of your hard-earned real coins into it! Warframe has a wonderful community driven economy, and if you can find things to trade with other players, then you can earn platinum that way.
The trade system in Warframe can be very good and resourceful, but in my experience, the prices in the game are either overpriced or people expect you to give them your stuff at too small a price. I recommend to any Warframe gamer to use https://warframe.market/. It is a website that is actually linked in with the official Waframe website and is the best way for you to see the general prices of items without being ripped off in any way. It is really easy to use and you can announce that you are online in game and list all of your items whether you want to sell or buy them.
How to trade with other players is simple enough. You can either go to Maroo’s Bazaar on Earth and hope someone wants to trade, or you can invite players to your Dojo or have them invite you. This approach is much simpler and quicker. Making a Dojo is super easy, as you simply go to communication and then Clan in the options menu and it’s straight forward from there. You just need to gather resources for your trade post within your Dojo and there you have it!
Prime items are what you need to earn that lovely platinum! Prime is in basic terms, better versions of the normal Waframes and weapons etc that you can already receive. These are much more sought out and are the ONLY things you can trade except for MODS. And thus, they are the items you should be trying to gather.
Void relics is your source of platinum. Especially for anyone starting out! Void relics are the items you can get by doing missions such as defence and excavation (Each mission on each planet has a mission type). You then crack these open by doing fissure missions and completing them, which gives you a prime item that can then be traded for platinum.
For those who are desperate for those wonderful in-game marketplace cosmetics, don’t worry! Remember, you can earn as much platinum as you want without forking out! Just be patient and keep farming those relics and you’ll be fighting for the Tenno in style!