In the Finder you can just go to MacintoshHD..Users
I totally get your confusion! I was similarly confused...when I opened my finder I didn't see user, yada yada yada...But there was a little house with my name on it. I clicked on it. I was the user. See if you can find the house in the finder drop down menu. That could be you, the user! Whew! But before that, I would print out the instructions above on a separate sheet to refer to because they are very exact and will work. Trust me. I am 69 years old and I managed to do it. But only exactly as they outlined above in the Importing Photos from Lightroom instructions.
OK. Back to work. Once you find Yourself, look for Pictures, then I Photo Library as they instructed. CONTROL click the IPhoto Library file and select Show Package Contents. Look for a folder called Masters, CONTROL click it and choose Duplicate.
Drag that folder to your Desktop and then Lightroom will be able to see it.
Then open Lightroom and drag the Masters copy folder into the GRID view of its Library module. The import window will open, with your iPhoto files selected.
I did that and then freaked out because they all looked all grayed out!! Aargh Well, I only had about 4000 photos and it just took a while. Luckily, I didn't throw my computer at the wall right about then, I just noticed that if I chose the Loupe view I could see one of them....then more...
And now one year of my photos are in Lightroom for me to work with between Lightroom and Photoshop.
I highly recommend the Adobe Classroom in a Book Series for superbly detailed instructions on Lightroom, Photoshop, and one of my personal favorites, Lightroom and Photoshop for Photographers, which carefully teaches the workflow between Lightroom, Photoshop, and back again.
Gee, I hope that helps! The whole thing can make us feel really stupid until we get it!
But it is there to "get". Wishing you well.
p.s. the "control" clicks are really important