Schematics are a set of plans that crafters use to create in game items. There are lots of stores which sell schematics i.e. Warstrider Schematics, Mero Brothers Schematics, Universal Construction, Coopers Schematic Supply, and Arc-Light Projects to name a few.
A player can buy these schematics at any time but must have the requisite Production and Manufacturing skills to produce the item listed in the schematic.
Also, a player must buy, extract, or trade for resources required to craft the item and may have to buy, make, or trade for any component items listed in the schematic. Oftentimes higher level schematics (that is, those requiring many smaller items to be crafted, traded, or bought before crafting the finished product) also require buying or making the sub-components.
See this Crafting Guide for more information.