Fabrication in HS is pretty much like crafting and follows couple rules, still sometimes it is not easy to tell how and why you can or can't improve your items.

General

To open fabrication window type /fabricate or double click fabricate in actions tab.

What you can do:
- improve weapons (increase damage,  decrease delay, add effect)
- improve systems (increase existing stats, add new stats)
- create new ammo or fuel
- create new weapons and systems

What you need:
- alot of time
- weapon/system you want to modify
- specific parts that drop from mobs
- upgrade kits (can be bought from starbase lvl2 shops)
- enchanting stones (drop from bosses)
- tech requirement reducing stones (drop from bosses)

Recipes:
- alpha fabs - check other guides
- plussing - you need 2 items that have same id and 1 upgrade kit. To know what type of kit you need select item and press Activate. Eg. Put together in fabrication window, not stacked: stella bay, stella bay, simple kit then press fabricate.
- enchant - fab together item and stone
- create new weapons - weapon core, weapon mold, conduit, skill (skill optional, all other required)
- create new systems - system mold, conduit, system attributes (up to 4 sys attribs, you have to match location with mold)

Limitations:
- you can only stone an item ONE time
- systems with 4 stats cannot be stoned
- you can plus an item up to +9
- created items cannot be stoned
- items bought from starbase shops cannot be modified
- ALL plussings have a max of 95% success rate

Weapons

It is recommended to farm for materials and money before you start fabricating as upgrading kits will be expensive in the long run.
Raising skill can be done via plussing, stoning or new fabs.
General plussing: weapon weapon kit
Tech needed for high success chance can be found in the brackets if you activate a weapon (weaponery skill 14)  eg. or you can check weapons lvl then add 10%, rounded down.( For example to plus a lvl55 brekkar laser you will need 55+10%=55+5.5=55+5=60 skill for high  success chance.)
On every plus you will gain a 10% damage bonus, rounded down. Eg. 25/30 wep will gain 25*10%=2.5=2 so +1 of that will be 27/30. However, the next plus, formula is applied again on BASE stats (25/30) so at +2 we have: 25*20%=5 so wep will be 30/30. (Not 29/30 as when you add 10% rounded down again) So keep in mind that leftovers carry over plusses but will only be added when them reach 1. (0.9 will still be discarded)
You will gain skill from plussing a weapon up to 10.0 skill over the required skill. Eg. While plussing brekkars to +1 you can gain skill up to 70.0 (60.0 needed) - this needs more testing but looks to be true from observation.
Stoning a weapon will raise a weapon's lvl if dmg raised or delay reduced. However adding effect to a weapon can lower its lvl as some weps have their lvl rounded up.(eg. brood laser is lvl50 but when stoned with effect will change to lvl49)
Quantum stone - reduces tech needed by 33%
Infusion stone - reduces tech needed by 50%
You can plus a higher tech weapon by adding one quant/infusion stone into the fab: wep wep kit quant. Eg. you need 64 tech to plus Bxirs but you only have 50.0 skill. When you add the quant stone, your new tech requirement will be 64-(64*33%) or 64*0.67 for easier math = 42.0. Success
You cannot use quant/infusion stones to stoning fabs, only to plus.
Always keep in mind that for a tech 50.0 fabrication, if you have 50.0 skill, your success chance is 80%. You can raise this chance with intelligence stat (every 5 INT adds 1%) or with stats on weapons (new fabs) but will never be higher than 95% for plussing.
Stoning success chance can go up to 100% and it is the same for all items regardless their lvl(boosted for items under lvl30). Eg. you have 50.0 skill and 40 INT. Stoning a weapon lvl50 or a weapon lvl142 have the same success rate = 50% from skill + 40/5 from int = 50+8 = 58%.
If you plus a weapon then stone it, you can still plus it further. Note: on more plussing, bonus added will still be the one from original weapon, not from stoned weapon.
New fabrication weapons are divided in 2: ammo based (launcher and bay) and energy based (all others).
Ammo based: ballistic framework + launcher/bay mold + conduit + skill
Energy based:  molecular coil + beam/disser/bolt mold + conduit + skill
Skill added is optional.
You have to match weapon's core lvl with the conduit.
Skill have an increase of 15 lvls for every +1 skill. Eg. if you want to add +3 tactics on a new weapon, that will require weapon core+conduit to be higher than lvl45 (because +3 tactics require 3*15= at least lvl45).
Skills for weapons drop only from bosses as of now.
You cannot add wep cores or skills to already existing weps, only create new ones with them.
Tech skill needed to make new fabs is generally wep cores lvl +5. (Eg. For wep core lvl53 you need 58 tech).

Systems

All rules from weapons (plussing and stoning) apply to systems too.
While plussing systems, all stats existing on an item will get a 10% increase. Eg. Dread plate: 25sa 25off 2 rech 10def. +1 will be 27sa 27off 2 rech 11 def. At +2 we have 30sa 30off 2rech 12def. So, to gain 1rech more, we need the plate at +5(for the 0.2 increase per plus to add on plate).
Plussing cloaks will decrease cloaking time by 5%. Eg. Cloak 10sa cloak100 will be at +1 11sa cloak95.
Pick your systems wisely as 4 stats items cannot be stoned.
New fabs: sys mold + conduit + sys attrib
You can add up to 4 attribs to a newly created system, tho them must be all uniques (eg. you cannot add 2 hull attribs to same item).
You have to match highest sys attrib's lvl with the conduit. (Eg. comp mold + sys attrib lvl30 + sys attrib lvl48 + conduit lvl41-51).
You have to match all sys attribs location with mold. (Eg. You cannot add an attrib that has location sensor to a computer).
  You cannot add sys attribs to already existing systems, only create new ones.
Tech skill needed is generally highest sys attrib's used lvl +5. (Eg. Attribs 20/34/60, we take into account the lvl60 attrib so you need 65 tech).

You can try all fabrications with lower tech skill in the hope of skill gain, not recommended if you wish to keep the end product, as success chances will be lower.

To be updated.