While on Avalon and before deploying, you may add Crafter Programs to the Crafter section of your Loadout. You can then use these programs during deployment to quickly convert Nanites into usable items and equipment.
Once you have deployed with your chosen Crafter Programs, the default key to open the crafting menu is (Z). Select the program you would like to use by hovering over it with the mouse and holding left-click will complete the crafting process.
The craftable item will be shown in Green if you have the needed Nanites to create it, and Red if you do not.