As a preposition, "on" has various uses in English. Here are some of the most common:

1. To indicate physical contact or attachment:

• The book is on the table.
• The painting is on the wall.
• The sticker is on the car.

2. To indicate a location or position:

• The store is on Main Street.
• The hotel is on the beach.
• The restaurant is on the second floor.

3. To indicate a surface:

• There is a stain on my shirt.
• The icing is on the cake.
• There are buttons on the jacket.

4. To indicate a state or condition:

• He is on vacation.
• She is on the phone.
• The computer is on standby.

5. To indicate a topic or subject:

• Let's talk about what's going on.
• We had a discussion on the new project.
• The article focuses on the benefits of exercise.

6. To indicate a means or method:

• She travels on foot.
• He sent the documents on email.
• The package was delivered on a truck.

7. To indicate a time or date:

• The meeting is on Monday.
• The event is on December 24th.
• The concert is on at 8 pm.

8. To indicate an ongoing action or process:

• She is working on her project.
• He is studying on his computer.
• They are focusing on their goals.

9. To indicate approval or support:

• I am on board with this idea.
• The committee is on the proposal.
• The manager is on my side.

10. To indicate something that is displayed or shown:

• The picture is on the screen.
• The movie is on TV.
• The news is on the radio.

It's important to note that "on" can have other meanings and uses depending on the context, so it's always a good idea to check a dictionary or language reference when in doubt.