Revenant stances
Go to your hero panel and begin too unlock the legends by spending your hero points.
A lot of content is gated to prevent new players from becoming overwhelmed with the onslaught of information presented to them. Like it has already been suggested, you should be able to invest into different stances through the use of your hero menu and the training system. Once you have unlocked multiple stances you will be able to swap them freely just above your weapon bar by clicking on them (like you would for normal utilities) and switch depending on what you have unlocked/desire to use.