This added content isn’t available right away, and with good reason. You will need some major gear and a lot of understanding of your skills if you are going to make any kind of headway in Crucible.. Once purchased, your first chance to take on the trial comes after Act 1, basically after finally reaching the Tree of Life in the Forge Lands.
You receive an invite to a strange tournament where wave after wave of the enemies that you’ve faced are thrown at you and your only goal is to take out the enemies and make it as far as possible. There are 100 waves in total, and at the end of each 25 waves, you will be granted special gear that will greatly increase your stats.