Hammer Editor 4 Input/Output Tab Tutorial
(note: this is not as much step-by-step as it is general how-to)

The input/output tabs in the HL2 version of Hammer confused me a little at first, but with a little playing around they emerged as an easy-to-use way of linking multiple entities. First is a list of the names and functions of the buttons in the tabs:

Outputs:
Mark - "Marks"(in other words selects) the entity affected by the currently selected output, and centers it in the 2D views.
Add - Adds a new blank output to the currently selected entity.
Copy - Copies the contents of the currently selected output to memory.
Paste - Creates a new output using the contents in memory.
Delete - Deletes the currently selected output.

The Inputs tab only has the "Mark" button, which goes to the entity that the currently selected input is coming from and centers it in the 2D views.

Most of the options after you add an output are pretty self-explanatory, and there are some different ones for different entities. All you have to do is add an output, select what triggers it, select what entity it affects and how it affects it.

For example: create a func_button named button01 and a door named door01. Go to the flags tab for door01 and check start locked. Add an output to button01 with these properties:
My output named = OnPressed
Targets entities named = door01
Via this input = Unlock

And there you have a door that must be unlocked by a button before it can be opened. There are much more complicated things you can do with the output/input tabs, and with a little bit of tinkering and work you can create large chains of events that both look and work great. The possibilities for a single button are immense, provided you link things together.

Iceman:

using the multimanager is a good example of what values can do. If you add a value to the same name as a triggerable (func_button for example) then when the multimanager is activated it waits as many seconds as the value and then activates it, and if you add another value linked to the same button it will wait that many seconds to trigger it again. I'm not good with words, hope I didn't confuse you more.

Just one question if you unclick smart edit and then add a value is there any way or any thing that value can do?

The old "Target" hasn't changed. It's still in use through Quake 3 (and it varients - Fakk, CoD, ect) and into Doom 3 as well. This tutorial was great to get me going.

The I/O is is really big improvement over the 'Target' in half-life 1

Yeah, i thought that looked a bit off... points for consistancy? anyway, fixed!

i know this tutorial isnt the most in depth, and the topic it covers is mostly self-explanatory, but i said i would write it, and there are many people who dont have HL2 yet who would like to know this info. plus, now that its done nobody else here has to do it.