If this is your first time launching a collaborate session then you will need to install the Collaborate Launcher.
Once Collaborate Launcher is installed.....
To join a "live" session:
Go to the Blackboard Collaborate link in the Blackboard site you are expecting to attend the session in and click the session link then click on "Join Room";
if you have been sent a specific link click that link).
Depending on your Browser settings it will either open the meeting.collab file directly using the Collaborate Launcher, or it will download a meeting.collab file to your default Download directory, in which case you will need to double click on the meeting.collab file to run it.
For information on Playing a Recording please see Play a Collaborate Recording