The 1-on-1 section can be found within the home panel. First click on the Home icon in the navigation bar (the house icon)
When you open the Home panel, you should be able to see everyone who you have 1-on-1s with. These 1-on-1s might appear in either your Starred or 1-on-1 sections, depending on whether of not you have starred the stream.
And to make it easy, the 1-on-1s that you have scheduled today will appear under the Today's meeting section to make it easy to navigate to.