Du vs Sie
Direct translation is "you" for both, but but different verb form is applied...hmm I'm confused now.
The lowercase 'sie' can mean 'they' and will use the same verb conjugation as the formal Sie so it depends on the sentence context. I can't seem to find the example using your link...
Du is you, Sie is she if we are talking informally. But Sie can be used also as formal "you" in singular and plural. For example: Haben Sie das Geld? - Do you have the money?
Du is for people close to you, children, people who have given you permission to use du. Sie is more formal.
Both of the above posters are correct. Du is the informal version of You. Sie is the formal version of You, however it can also mean 'she' or 'they' depending on the context. For example, using the sentence from dejan, Sie haben das Geld means You have the money or it can also mean They have the money. If the verb was conjugated differently, you can tell when it means 'she' for example Sie hat das Geld. She has the money, the verb will be conjugated to match subject being 'she' instead of You or They which would use 'haben.'