Like many other languages, German has formal and informal ways to address people:
you (plural and formal)
In business or professional environments, German-speakers tend to be more formal and reserved than people in some other 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 how old people are. Younger people are more likely to use du instead of Sie.
It is better to risk being too formal rather than being too familiar. When in doubt, use Sie. If you get it wrong, 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 verbs in the formalSie is much easier than the du conjugation. To start with, it is almost always regular!
There is one notable exception to this regularity of conjugation in the courtesy form "Sie": the verb sein (English: "to be"). Sein is irregular and has to be learned separately particularly because in this sense, it is also unique!