Polite forms
The distinction between polite and informal is much more pronounced in Japanese than it is in English. Not using the polite form while talking or writing to a stranger or superior is extremely insulting. Mastering the correct level of politeness is of paramount importance when communicating with the Japanese.

Here we will focus on the most neutral form of politeness, the honorific and humble forms will be discussed in later lessons, since they are probably the most difficult part of the Japanese language. Most of the time you'll be able to get away with using this form though.

There are two distinct forms of politeness. Being polite when talking to someone, and being polite when talking about someone or something. The honorific forms we've seen so far: The honorific prefix お… and the honorific suffix …さん are polite when talking about someone or something. These words are sometimes translated as "honourable" in movies or cartoons, but should normally be left out of the translation, since the English language doesn't have words that can be used in such situations.

The "-masu" (…ます) form
The "masu" form is the general polite form. It is neither humble nor honourific, and is used when two people are of the same status, or when the status of the other person is not known. This form is polite to the person you are speaking to, it is not related to the topic of your conversation. This translates to speaking to colleagues, people on the street, and on the telephone. Almost every verb can be made polite by adding …ます (masu) to the ren'youkei conjugation.
Note that the "u" on "-masu" is silent.

As you can see, the translations stay the same.

Desu (です)
There is only one exception: だ (da), which has as its polite form: です (desu). As explained in the third lesson, だ is a contraction of である (de aru). です is also a contraction, in this case from the extremely polite でございます (de gozaimasu). This extreme level of politeness is lost when it is contracted into です, and the verb takes on a neutral level of politeness, the same as …ます.
Note that the "u" on "desu" is silent.

Time
Words indicating time are followed by the particle に (ni). Words indicating a period of time rather than a specific point in time are preferably used without the particle. These words include "tomorrow", "today", "this morning", "last year", "every month", et cetera.

For some statements of time more than one pronunciation exists. As a general rule, the Chinese reading "音読み" (on'yomi) is the formal reading, the Japanese reading "訓読み" (kun'yomi) is the normal reading.

In some cases, the on'yomi can have a different meaning:

The particle の as a relative pronoun
An important function of の (no) is the relative pronoun. I have briefly touched upon this point in lesson 1, but I will further elaborate on it here.
When used as a relative pronoun you can usually translate の as "which is" or "who is". The second statement is described by the first statement.

Sometimes the relative pronoun seems superfluous in English, in these cases you can replace the explicative with a single word.