As in many other languages, German has a formal way to address people:
you (plural and formal)
In business or professional environments, German-speakers tend to be more formal and reserved than people in the Americas or other European countries. The formal Sie is used to address strangers, business associates, and acquaintances.
Students or co-workers, most frequently address each other as du. But this may depend on the particular company culture, the degree of intimacy and the age. Younger people are more likely to use du instead of Sie.
It is better to risk being too formal rather than too familiar. When in doubt, use Sie. People might quickly offer you duzen, which means you can address someone with du. There is also the counter-part siezen, which means to address someone with Sie.
Tom, du kannst mich duzen.
Tom, you can address me with "du".
Good news on the grammar side
The conjugation of Sie is much easier than the du conjugation. To start with, it is always regular, always!
Wow, that's much easier than I expected! Especially that it's always regular!
Okay, I shouldn't have been so emphatic about the "always". There is one exception: the verb sein (English: "to be"). But that's the only one! More about that soon.