How long does it take for me to be able to trade?

I just created an account, too. Apparently you need 15 posts to add images (cig). You can use Ladder Slasher market off the bat.

You can start trading right away, just find the game you're looking for and make a topic, or search through existing topics.

Here is a new user guide, with a lot more information that you might find useful. https://forums.d2jsp.org/topic.php?t=63392948&f=34

Also I would suggest using a mediator for your trades to prevent scams. It's fast and free