Replacing HDD for beginners

A lifelong fiddle-ophobe, I have recently upgraded my RAM smoothly and with great success. My new hard drive has arrived today and I am just about to replace it. One last question:

rather than cloning my old drive, I want to do it with Time Machine. Could one of you knowledgeable people talk me through this? When I start up with the blank drive inside, I read something about having to partition it first, but I have no idea what that means? When exactly do I connect the external time machine drive? Before I even turn the machine on, or after I've partitioned it (and turned it off again?)

Thank you for being so patient with me!

edit: will I have to put Lion recovery assistant on a USB stick first?

 

worked it out it seems