Ok, so I have done some extensive Googling and have been unable to find any help that doesn't assume I have been building maps for some time (this is my first try). This is probably the most "Noob" question possible, but can anyone help me with linking two doors (enter/exit) together? I'm talking the basic, get off the elevator and there is the door to the first chamber. All I get is either the door opens and their is a big black nothing that I can't even walk into or the door simply doesn't open.

I can't seem to wrap my mind around where/what I need to do to for this and I can only figure it is something terribly simple that I keep overlooking. Thank you anyone that can drag my sorry butt out of the dark and help me so I can move on to the next problem I can spend way too much time figuring out

For some stuff it's good to look on youtube. Here is a tutorial on buttons and doors. Also, here is a tutorial to make the doors automatic rather than through the use of buttons.

The stock instances are set up with a solid brush in them. You can either edit the instance you are using, or use a linked_portal_door inside the opening of the door you are using.

Ah, the 'big black nothing' happened to me - I'm assuming you're using the door instances, right? Well, the door frame instances aren't actually usable in their untouched state; you need to delete the back of them, because they're entirely solid! Bravo, Valve... I don't know about e 'door not opening' thing, though, sorry.
EDIT: Gah, beaten to it by a minute!

Valve was fairly sloppy with their instances in general. Carve tool and all that.

Instead of using door instances, I copy and paste the door (with frames) out of the zoo mechanics map. That way you don't have to do anything but fit it into the wall and make a trigger or button to open it.

Incredible, this is by far the most useful and friendly forum I've been on. I'm going to work my way through all the suggestions and see what I can learn (and hopefully accomplish finally )

Great links Lostprophetpunk, I've seen the button video but never managed to come across the trigger video, that one might help a lot next chance I get to watch it and test it out.

Marlovious, I did try the linked_portal_door but unfortunately I think part of my failures is related to my lack of knowledge in the instance/entity settings fields. I can't seem to figure out where I need to go to actually link the enter with the exit.

Ok, Rubrica and Vordwann, I might be dense on this, but how do I delete the backing on the door? That seems like the quickest route since the doors still appear to open for me, but I'd assume I would still need instancing to lock the door once past it correct?

Marise, I have tried something like taking a door from another map but just ended up confusing myself more somehow. Maybe I'll give it another shot with the zoo mechanics map though, I haven't even really given that one a solid glance yet.

Thanks to everyone so far for all your help! All these ideas are hopefully going to bring me closer to just maybe creating something at least half as awesome as some of the maps I've downloaded and played off here that got me intrigued in mapmaking in the first place

To delete the backing, try using the "Move to World" button on the top right of hammer in the interface while selecting everything in the instance file (open it from the folder). Then select the wierd back part and delete it. After that, click on the part that is just the door frame and press the "Move to Entity" button or control T.

Why Move to World? I just deleted it instantly without moving anything to the world, and mine work perfectly.

Oh I assumed it was everything converted into a func_detail. Yup. Sorry. Just delete the back.

Thanks Rubrica and Vordwann, I will have to give that a try later and see how it works. I watched the link to the door video from Lostprophetpunk and now have a working door so I can finally move on to other things (incidentally, I now also understand linking triggers to props which circumvents other issues I was going to have) Thanks again everyone for your help!