'to set something off' means to cause it to start or happen.
- The smoke form my cooking set the smoke alarm off.
- The proposals for a new shopping centre have set off a very heated debate in the town.
'to set someone off' means to start them laughing, crying or talking.
- Every time Jake used that silly voice, it started me off laughing.
- Kelly started crying and that set everybody off too.
'to set on' means to begin a physical attack.
- If I went into the garden, she said she would set the dog on me.
- Coming out of the pub, he was set on by a gang of boys and his money stolen.
'to set out' is to start on a journey.
- We wanted to get there before lunch so we had to set out just before dawn.
- They packed their bags and set out early as they had a long walk.
'to set out' to do something means that you have a clear idea of what you intend to achieve.
- We didn't achieve what we'd set out to do.
- He didn't set out to invent the microwave oven. He discovered it while doing other research.
'to set out' facts or opinions is to explain them clearly in writing or in speech.
- All the terms and conditions are set out in this document.
- Your terms of employment are set out in your contract.
'to set something out' is to organize it so that it is ready to use.
- When I arrived all the materials and equipment were set out ready for use.
- The chairs were set out in a circle ready for the class to begin.
'to set up' means to start a company or organization.
- After a few years developing the products, they needed to set up a company to sell them.
- The UN was set up when representatives of fifty countries signed the charter in 1945.
'to set up' also means to make arrangements for a meeting, a committee, or an investigation.
- I'd like to discuss that in more detail. Can we set up a meeting with everyone concerned?
- The government has set up a committee to investigate possible fraud.
'to set up' a structure or building means to erect it.
- It took almost an hour to set up the tent in the rain.
- The Police set up road blocks throughout the county to try to find the thieves.