Your basic starter for 10.
History and Functions
iChat is an Instant Message Application.
It has been around in one form or another since 2004.
Initially it could only connect to the AIM servers ( Apple had an agreement for Apple IDs ending in @mac.com (at the time) were also Valid AIM Screen Names. Later, with MobileMe being released, @me.com names also became valid)
iChat 2 essentially added Video and Audio chats. (This was free in Panther. There was a demo and a purchasable version before that)
At iChat 3 (Tiger) added Jabber accounts (These included GoogleTalk and Facebook IDs as well as Jabber IDs registered elsewhere)
Adds 3 and 4 way Video Chats and up to 10 people, including yourself for Audio Only chats
iChat 4 (Leopard) separates out a Googletalk Set up option in the Add Screen Name panel.
Add Video Effects and Backdrops (PCC computers can not play Backdrops).
Adds iChat Theatre and Screen Sharing.
Adds MobileMe (@me.com names as an option in setting up an account (Adding Screen Name as an iChat "Account") )
iChat 5 (Snow Leopard) changes the Add Buddy pane for the AIM Buddy lists. Before you had to list @mac.com and @me.com from MobileMe where as in iChat 5 they are added as their full name (email@example.com for instance)
There is little other changes at this time.
iChat 6 (Lion) again changes very little in layout and the way it works although it does add the ability to use a Yahoo ID in iChat.
Messages Beta is current at time of writing and is credited with being version 6.1.
It allows iMessages to be sent to Phones and iPads (iOS 5 devices) as well as working the same Buddy Lists as iChat.
For iMessage Contacts it will invoke the FaceTime App to enable Video to the Phone Number or Apple ID (which could be on a Phone or iPAd or to theFaceTime for Mac app)
iChat can send Text (IMs) to Buddies on a 1-1 basis or in Group Chats (Chatroom).
It can Send Files (iChat to iChat) and to some Applications on PCs and Macs (Web Browser Logins for some Accounts/IDs are more difficult).
These can include Pics-in-Chats where the pic in displayed In-line (It is scaleable on dragging the window bigger) and be "Saved" if dragged to the Desktop.
iChat can Save Text chats.
It can also do Audio Only chats and Video Chats and with some these can have mulitple people involved.
At iChat 4 (And after) you can alter the Video feed with Effects and Backdrops.
Also iChat Theater allows Documents from other apps to be the Video Feed (as in Keynote or Powerpoint Presentations) It can also access the iPhoto Library and do Slideshows.
What you need.
A Mac with a camera and Mic (Or access to those externally: Mac Pros and Mac Minis don't have cameras or Mics)
An Internet connection with at least 256kbps as both Upload and Download speeds for Video Chats on a 1-1 basis.
Good Lighting if using the camera.
A Screen Name or ID from either AIM or a valid Apple ID (Keep the password to 16 characters or Less as this is the AIM limit) or a Jabber ID from a Jabber server (or Google Talk or Facebook) or Yahoo (iChat 6).
This can depend mostly on what service your Buddies are using.
Apple IDs from iCloud will not work in iChat 5 or Lower.
This is because iChat 6 does a double Login to both AIM and Me.com.
The me.com login allows the AIM server to "See" the password and log the ID/Screen Name in to the AIM servers. iChat 5 and earlier do not make this me.com login so the password cannot be verified.
Registering an @mac.com or iCloud @me.com name encourages your to make a Secure password and hints at longer ones
The AIM servers can only cope with passwords up to and including 16 characters.
You ideally need another email for Confirmation and Password recovery (you can use the same email as many times as you want to set up AIM names)
Don't skimp on setting up the security questions for Password recovery.
It can pay to Screen Shot the page and send that to yourself in an email just so you can remember what question it was at a much later date.
Used to be names issued with the .Mac service (Forerunner to MobileMe and iCloud) and now offered as an iChat name.
Keep Password to no more than 16 characters
You will need an Email.
This cannot be one already linked to an Apple ID (the @mac.com name is an Apple ID and you cannot create one Apple ID with another)
For this Reason the secondary Email can only be used Once.
MobileMe is being replaced by iCloud at this current time. (Older style @me.com names)
New names and iCloud ones also end @me.com.
As mention earlier these will not work in iChat 5 or earlier.
Again the password cannot exceed 16 chararcters.
The External (to Apple) email can only be used once.
You can link an existing Apple ID you have to an iCloud name.
You may have an iTunes Account based on your ISP email ID and you can link this to an iCloud ID
If you already have a Google Mail ID then if you Enable "Talk" on your Google settings you will have an ID that can be used as a Jabber ID in iChat.
The process is similar for Facebook names once you have enabled "Chat" in your Facebook Settings.
Registering other Jabber names tends to take a 3rd party app.
This is because the registration process happens with those apps and not in a Web Browser On line (Jabber Australia is the one place I know is an exception other than Facebook or Google)
If you have not already got an ID or Name then register a name.
In the Start up Screens enter the Screen Name or ID you set up.
Add Buddies to the List.
Text chats take a double click of the line the Buddy is On.
Video or Audio chat can be started by the green icon that shows (Highlight Buddy and use the icons at the Bottom of the Buddy list is one way to do Audio only if showing a Video icon.
Please, if posting Logs, do not post any Log info after the line "Binary Images for iChat"
iMac 2.5Ghz 5i 2011 (Lion 10.7.3)
G4/1GhzDual MDD (Leopard 10.5.8)
MacBookPro 2Gb (Snow Leopard 10.6.8)
Mac OS X (10.6.8),
"Limit the Logs to the Bits above Binary Images." No, Seriously