Hi,
The Messages app can use different ID to use the different services.
It can use Apple IDs to use the iMessages service (Text Only) But you can invoke FaceTime from an existing conversation.
By default you also get the Bonjour Account.
If you have other Macs on your LAN (and they use iChat or Messages with Bonjour Enabled) you can Screen Share with them (in addition to Video Or Audio Only chats).
You can join the AIM service with some Apple IDs (ending in @me.com and @icloud.com in most cases and sometime @mac.com depending on your OS version) and of course with AIM or AOL registered Screen Names.
Mac to Mac (iChat or Messages) these can Screen Share over the internet.
Whilst the Login may be SSL (AIM almost insist on in nowadays) the Video chats, Audio Only chats and Screen Sharing are Peer-to Peer connections.
There are steps in the connection process to make sure you are not vulnerable to "Man-in-the-Middle" attacks.
They will only work AIM to AIM.
Jabber (Or XXMP) accounts can include GoogleTalk or Google Mail IDs in reality or Facebook chat IDs are valid Jabber IDs.
You can of course register for a Jabber ID on any other Jabber server you know about.
These will work Jabber to Jabber must be to a Mac using iChat or Messages and not other apps or web Browser logins (As you can do with both Facebook and Google).
The Yahoo account is text only.

8:55 pm Wednesday; July 16, 2014
iMac 2.5Ghz i5 2011 (Mavericks 10.9)
G4/1GhzDual MDD (Leopard 10.5.8)
MacBookPro 2Gb (Snow Leopard 10.6.8)
Mac OS X (10.6.8),
Couple of iPhones and an iPad