The usage and examples of quotation marks are as follows:

1. Direct quotation.

When quotation marks are used to directly quote someone else's words, double quotation marks are usually used. For example:

Read thousands of volumes and write like a master. This is a famous saying by Du Fu, a poet of the Tang Dynasty.

In this example, quotation marks are used to directly quote Du Fu's poem.

2. Indirect quotation.

When quotation marks are used to indirectly quote someone else's words or express their meaning, single quotation marks are usually used. For example:

He said that the company will continue to work hard to create high-quality products.

In this example, quotation marks are used to indirectly reference the company's commitment to the product.

3. Emphasis.

Double quotation marks are usually used when they are used to emphasize a word or expression. For example:

At this special moment, thank you is particularly important.

In this example, quotation marks are used to emphasize the importance of the word thank you.

4. Special meaning.

Double quotation marks are usually used when quotation marks are used to express special meaning or sarcasm. For example:

He is a genius, but his genius is only reflected in bragging.

In this example, quotation marks are used to indicate the irony of the word genius.

5. Proper nouns.

When quotation marks are used to express proper nouns, single quotation marks are usually used. For example:

His name is Zhang San.

In this example sentence, quotation marks are used to indicate that Zhang San is a proper noun.

The functions of punctuation marks:

1. Sentence breaking: The most basic function of punctuation marks is to break sentences. By adding punctuation between sentences, we can divide a long sentence into several independent short sentences to express ideas more clearly. This sentence segmentation helps readers better understand and remember the content of the text.

2. Tone emphasis: Punctuation marks can be used to emphasize the tone and emotion of a sentence. For example, exclamation points and question marks can express a strong exclamation and questioning tone respectively. By using these punctuation marks, authors can better convey their emotions and attitudes.

3. Semantic distinction: Punctuation marks can help distinguish the semantic meaning of a sentence. For example, commas and pauses can be used to distinguish different components such as subject, predicate, and object. This helps readers better understand the structure and meaning of sentences.

4. Logical relationships: Punctuation marks can also be used to express logical relationships between sentences. For example, using semicolons can distinguish several parallel sentences, making the article more clearly express the author's thoughts and opinions.

5. Clear expression: Another important role of punctuation is to make expression clearer. By using punctuation marks such as commas, pauses, colons, and parentheses, we can list multiple items, supplement explanations, or explain previous content, making the article easier to read and understand.