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The most fundamental part of Armstech crafting will be crafting various kinds of Assembly Elements. We'll begin by crafting an one of the default schematics you got when you selected Armstech, which as soon as you click it will inform you it needs 2 x Silica, 2 x Desh, and 2 x Conductive Flux to craft.

To determine which gathering skill the products you will need come from, hover over the noted product. When The Latest Info Found Here take a look at the tooltip by hovering over them, The Silica is listed as Grade 1 Scavenged Component and the Desh is Grade 1 Scavenged Metal both of which come from Scavenging.
White-bordered products are a bit different you can either send your companions to collect them if you have a mission readily available for them, or buy them straight from a vendor called the Crew Abilities Trade Supplier in the Strongholds & Crew Abilities area of the fleet who offers them quite cheap.
As soon as your companion is finished crafting your schematic, the product will appear in your inventory and your crafting level will increase. Assembly Components are the structure blocks of Armstech crafting while they're quite worthless on their own, you can combine them with other materials to craft actual products.