Steam users by default are restricted from trading after account creation since new accounts are labeled as “Limited Users”.
To remove this restriction, you need to spend at least 5 USD on Steam by purchasing a game or gift card or topping up your Steam wallet. Also, keep in mind that parental control on Steam prevents your account from trading.
If you meet the requirements above, you can check your trading status by following the link.
You should see the following screen:
Important!
There are cases when your account will still be unable to trade due to a variety of reasons:
- VAC ban
- Steam trade/Community Ban
- recent mobile authenticator change/uninstall
- password reset
- other reasons.
All of the reasons are listed in Steam’s FAQs.
Some of them are temporary and/or require your action (for example, installing Steam Guard). Others are permanent and cannot be disputed (VAC ban or Community Ban).