How/When did Ezra Get his Green Lightsaber?

The lightsaber is a trademark weapon for those people who are in Force. In Star Wars, both Jedi and the Sith are identified by their glowing blades and which gets differentiated with colors or even by the designs of their lightsaber hilts.

But more often than not, a Jedi has loosened their lightsaber, or occasionally, it would be destroyed during dueling. It was the situation for Jedi where they are on a quest to build up a new lightsaber for themselves.

And, in the same manner, after the formal induction into the Jedi Order, A Padawan also had to build a new darksaber lightsaber. A Jedi keeps their old dark saber, or lightsaber, as their memory of their time as students.