Strand Sources are green fissures that will randomly appear in different locations on Neomuna in Destiny 2. When you bond with them, they will give you a 30 second boost to your strand abilities and also restore your abilities and super if you have the strand subclass equipped.
Strand sources are often found in high locations of the map, usually in some difficult-to-reach places that require a lot of high jumping and platforming in order to reach them. The video guide below will explain this better and show you how to find them and identify them.
Bonding with strand sources is required for the Maelstrom quest on Neomuna. You simply have to look within when you are next to a strand source to complete this objective.
Keep an eye out for the star icon showing up on the HUD to signal that there is a source nearby. If the icon is showing up somewhere high, this likely means that you have found it.