"Du siehst das Brot."
Think of Ihr as "y'all", or like a teacher addressing a classroom. If she said, "[You all] need to sit down," the words in brackets would be Ihr.
Lower-case "sie" is "she" or "they".
Sie (s.) (upper-case) is an honorific. In the workplace, it's still (mostly) considered good form to use "Sie" in place of "Du", until you have the "dutzen" conversation. It's going out of fashion with the younger generation, but I highly recommend using this as a foreigner. One would also use "Sie" with one's grandmother.
"ihr" is the plural form of "you", so it literally means "you all". When I'm talking to one person, I would use "du", and when I'm talking to multiple people, I would use "ihr". Make sure not to confuse "ihr" with "they" though, as the German word for "they" is different. I wish Duolingo would specify that this is the plural form of "you" each time the answer is given in English, as it is confusing. What I do to help myself remember the difference is go ahead and put "you all" when translating. You can also click "conjugate" when you hover your mouse over a verb, and it will show you the different forms of that verb for singular, plural, etc. I hope this helps!