You have to gather items from Ephemeral Nodes (The consolgames Wiki that the other poster linked is a great source - it says where / when each node pops)

When you first enter an area, the Node is already up. Once you've depleted that node, in order to get it to respawn, you have to hit two nearby nodes from two different 'sets' of nodes. I'm sure you've noticed the HW nodes all spawn in pairs - so just hit 1 from each of these and you'll force a NEW ephemeral node to spawn.

Now, as for the gathering from these nodes...

You use collector's gloves (Just like if you're gonna do Blue/Red g athering scrips) and then you need to aim for high collectability to get Landborne Aethersand. I tend to do a basic collectability rotation using two Utmost Cautions + 1-2 Impulsive Appraisals. If these two don't land a proc, I tend to abandon the node at that point unless I'm also going for Dusk/Dawn aethersand.

If one of those two do, I follow them up with a Methodical. The last two hits will be methodicals, one with Single Mind up, one with an extra Discerning Eye up. This will give you about 550~+ Collectability.

Aetherially Reducing these items has a chance of giving landborne.