The difference between masu-form and nai-form in Japanese

What are the difference between Polite and Plain Style.

Japanese can be divided into 2 types of speech - Polite and Plain Styles

The Polite Style can be used at any time in any place and to anybody. Therefore, the polite style is used most commonly in daily conversation between adults who are not close friends. It is used when talking to a person one has met for the first time, to one’s superiors, or even to persons in a similar age group to whom one is not very close. The polite style may be chosen when one talks to a person who is younger or lower in rank yet not so close.
Basically, both Polite-Form and Plain-Form can be divided into 4 groups: (1)Present Affirmative, (2) Present Negative, (3) Past Affirmative, and (4) Past Negative.

We will know if there is Polite Style when the sentence ended in です (desu), でした (deshita), ではありません (dewa arimasen), ではありませんでした (dewa arimasen deshita), ます (masu), ません (masen), ました (mashita), and ませんでした (masendeshita).

Usually ます-Form Verbs are the first thing that you need to learn when you want to know Japanese Language. Because ます-form verbs are quite easy to use and conjugate, and also because they are fairly polite.
The picture shows the example of Polite-Form.

The Plain Style is used when talking to one's close friends colleagues and family members. Note that you need to be careful about how politeness is needed, basing this on the age of your conversation partner and your type of relationship. If the plain style is used inappropriately, you could sound rough and impolite. So when you cannot tell the situation it is refer to use the polite style.

And it is commonly used in written work, newspaper, books and dictionaries. Thesis and diaries are all written in the plain style. Most letters are written in the polite style.
The picture shows the example of Plain-Form and how to conjugate in dictionary-form, nai-form, ta-form and katta-form.