Interjections

Interjections are words or phrases, usually placed in the beginning of the sentence, used to express emotion. It is commonly used in spoke language or informal communication such as texts, not professional social networking, and emails to friends. It is not recommended to use on formal writing such as business communication or scientific articles. Grammatically, interjections are not connected to another word of the part of speech.

• Yeah! Let’s do it. (agreement)
• Indeed! (agreement)
• Sweet! (positive feelings)
• Oh, honey! (pity)
• Aww (showing how sweet is it) 

Emoticons—a facial glyph used to indicate mood—are considered interjections: 

• :) (smiling)
• :( (sad)
• \o/ (celebrating)

Any word or phrase that captures an emotional burst, usually go as an interjection: 

• Yes, let’s go! (agreement)
• Agreed! (agreement)
• Nooooo (sometimes, sarcastic way to say “yes”)

The interjection mostly is followed by an exclamation mark to express strong emotion, commas and period to illustrate weaker emotion, and question marks to show confusion or disbelief.

• Oh, really? (disbelief)
• Yummy! (expressing that something is delicious)
• No, I don’t wanna do it! (disagreement)
• Well, I think that it is interesting. (considering)

You can see a dictionary of common interjections here and here.