All this data is potentially out of date, and should be taken with a truckload of salt
Tech 2 items are more advanced versions of Tech 1 Ships, Modules, and Ammunition. These items are usually more powerful or more readily available than their Tech 1 counterparts, but with greater skill requirements, more complex production steps, and consequently, greater expense.
Tech 2 Blueprints
There is a blueprint for every tech 2 item. A blueprint original or blueprint copy is required to produce the item. Most Tech Level 2 production comes from the Invention process, where Tech 1 blueprint copies are used to create Tech 2 blueprint copies which have extremely low Material Efficiency levels and limited manufacturing runs. Blueprint Originals do not have the creation hassle of blueprint copies, but the only way to acquire an original Tech 2 Blueprint is to buy one of the several blueprints already in circulation. These blueprints usually fetch prices in the tens or even hundreds of billions of ISK.
Tech 2 Materials
Tech 2 components need to be manufactured before the final Tech 2 items can be produced. Raw moon materials are reacted into basic products. The basic products are then reacted into advanced materials, which are used to construct Tech 2 components. These components, as well as Morphite, Minerals, and a Tech 1 item from which Tech 2 versions are based, can then be used to construct the final, usable goods.
Tech 2 Modules
Tech 2 Modules are usually just an improved version of their Tech 1 counterparts. The exceptions to this are Tech 2 Turrets & Bays, which are permitted to load Tech 2 Ammunition, and Covert Ops Cloaking Devices, which have vastly different functionality than Prototype or Improved Cloaks.
Tech 2 Modules can be identified by the II icon in the corner of their portrait. Tech 2 Modules also often have a Meta of 5.
For more information, see Module.
Tech 2 Ships
Tech 2 ships are much more than just an improved version of the Tech 1 ships they are based on - they often have a complete role change and capability to do things the Tech 1 ships they are based on cannot.
Tech 2 ships often have vastly increased resistances. They also have two ship skill bonus sets: one based on the Tech 1 ship skill, and the other based on the Tech 2 ship skill. For example, a Caldari Cerberus Heavy Assault Ship, a Tech 2 vessel, requires Caldari Cruiser to be at level 5, as well as at least level 1 in Heavy Assault Ships. For every Caldari Cruiser level, it gets 5% bonus to missile damage, as well as 10% to missile velocity. For every Heavy Assault Ships level, the Cerberus gets 5% to missile rate of fire, and 10% to missile flight time.
Tech 2 Ammunition generally comes in two flavors per Turret or Launcher type. For Turrets, there is a long ranged type and short ranged type. The long ranged type does decent damage, but can reach very far, while the short ranged type does the most damage of all. The long ranged type will usually have some small drawback to its use, while the short ranged type will have several drawbacks.
For Missiles, things are a bit different. For long ranged missiles (Light/Standard, Heavy, and Cruise), there is a damage type and a "precision" type. The damage type does extra damage at various costs (including a Capacitor cost), while the precision type has better Explosion Velocity and Explosion Radius at the cost of ship speed.
For short ranged missiles (Rockets, Heavy Assault Missiles, Torpedoes), there is a damage type and a long range type. The long range type has improved speed and flight time, to help it reach greater distances at a ship speed cost and damage cost. The damage type has improved damage at the cost of Capacitor, amongst many other things.