Use the Code Analyzer Tool. You should have it from the beginning on, but you can also buy it from an item vendor. To use it, you have to load Write Code and upgrade it everytime you level up so you get new abilities. Write Code maxes out at 15; that's the level where you can get Ability Maker, Tool Maker, Weapon Maker, Apparel Maker and Upgrade Maker. These abilities are at the very end of the Programmer tree and should also be upgraded.
To use Code Analyzer, drag it on your hotbar. There are categories you can select of, f.e. Ability Codes \ Coder or Apparel \ Pants and levels like 11-15 or 21-25. To code something, simply select it and press "Write Code". Abilities and other items are compiled from code fragments.
Green and blue fragments can be compiled from Code Bits, be bought from fragment vendors and received in missions (from corpses or containers).
Red fragments can't be bought or compiled, but you can still receive them in missions (although rarelier) or, and that's the common way, from certain gangs in the City. Use mxoarchive.com to check which gangs drop which fragments.
From what I know, you don't get red frags till level 20 (but I'm not sure, might also be 15 or anything). However, after that you'll need a lot of green frags and one red one.
If you successfully code an ability, it'll be placed in your inventory. Just upload it and it appears in your core abilities archive. If you code other items (like weapons), the code for the item will be placed in your inventory, not the item itself. Simply upload it and it appears in your compiling archive. You need the Compile Items ability and the Compile Tool for that. If not, you can compile it in the Loading Area.
There is another thing you should know: Writing Code (same as Compiling or Decompiling) can be either successful or not. If you fail, you loose your fragments but don't receive the item. Coding benefits from Reason, so think about upgrading this stat. Usually, if the "difficulty" of the ability is at the same level as you, you're likely to fail, but if you're one level higher, you should succeed.
There are buffed clothings that can increase your writing code abilities to 15+ levels and of course, guarantee success everytime you code anything. I don't know where to get it, simply look for it in the Marketplace or wherever else.
If you have any further questions, feel free to ask. Might just be that I don't know everything
