An assembly is a group of people or things coming together in one place.
Think about all the times you've seen groups of people gathering for different reasons - at work, in school, or even just with friends. When we need to gather everyone together, we use the word "assemble". For example, when a team of workers needs to put together a new piece of furniture, they'll assemble it by following instructions and using all the right parts. The same idea applies when people come together for meetings, events, or projects - we say they're assembling as a group. It's also used in more formal situations like a jury coming together to deliberate on a case or an orchestra gathering on stage before a performance.
To put together.
Example: He assembled the model ship.
