Simple Examples:
* Wow! That was an amazing performance.
* Ouch! I just stubbed my toe.
* Hey! Look at that bird.
More Complex Examples:
* Oh no, I forgot my keys!
* Well, I guess we can just order pizza.
* Goodness gracious, that's a lot of homework!
Note: Interjections are often followed by an exclamation point, but they can also be followed by a comma, depending on the tone and context.