One of the first things you will want to do in Destiny 2: Beyond Light is get your hands on some Stasis powers, so if you are wondering what to do, this guide will contain the good, and the bad, news.
To actual get your Stasis powers, you will need to play through the Beyond Light campaign. This is very similar to the launch of the game, when you unlocked your original subclasses over the course of the Destiny 2 campaign.
How long this actually takes you will depend on how quickly you can get through the campaign. Several portions of it have pretty substantial Power requirement jumps, and you will need to grind out other activities in the game to get new gear, weapons, and armor and increase your power levels.
You will need to talk with the Exo Stranger, interact with the new Darkness Monolith that can be found on Europa, and do plenty of other cool things before you manage to permanently unlock Stasis for your character. You will get to wield it from time to time throughout the campaign, often as a means of over coming the threat posed by Eramis and her various Lieutenants, so you will at least get a taste of that awesome Darkness power before you unlock it fully.
When you full unlock the Stasis subclass, you will also get access to new parts of the game called Aspects and Fragments. These important items allow you to customize your class how you see fit, and are an interesting new part of Destiny 2.