In Destiny 1, as you gained experience, your sub-classes advanced as well to allow you to unlock new abilities. In Destiny 2, they changed this to where you use upgrade points in order to unlock new abilities.
I started out as a Warlock, which begins you off with the Dawnblade sub-classes, but unfortunately, without realizing that the Stormcaller sub-classes isn't unlocked until later, I spent every upgrade point so far. Now I am wanting to save my upgrade points until I unlock Stormcaller, but I am also wanting to advance in the other sub-classes afterwards.
Based on this article, it mentions there are a multiple ways to getting upgrade points, but it doesn't go into detail of every possible way
Upgrade Points are earned in a variety of ways, including completing Adventures, but the easiest way is by leveling up
What are all of the ways to obtain upgrade points to advance in your sub-classes?