I know it is usually confusing which one to use in different scenarios.

Here are the best situations and general rules.

When talking about time, "in" is used to refer to a general, long period of time, such as months, years, decades, or centuries.

For example, "in April," "in 2015," "in the 21st century."

"On" is used to talk about particular days, dates, and holidays.

For example, "I went to work on Monday."

"At" is used to refer to hours, minutes, or very specific times.

For example, "The train will come at 10 a.m.," "He's still working at midnight."

When talking about space and address, "in" is used to refer to a large land-like area like city, states, countries, etc., while "on" is used to talk about street-level locations like road, avenue, etc.,

"At" is used to refer to a specific or concrete address, like street number.

For example, "Michael lives on 12th street in New York City."

"Her office is "at" 250 Market Street in San Francisco."

"Brazil is in South America."

You can see, "in" normally refers to a large space or long period, "on" is relatively smaller, shorter, but still not a concrete location or time, while "at" is the smallest and shortest: It often refers to a very specific location or time.

With this information, you can handle 95 percent of the use-cases, but you know, there're always exceptions in English, like when talking about surface, we always use "on."

While we use "on" when referring to days, "in" is used for parts of days, like "in the morning," "in the afternoon," etc.

We hope now you can use "at," "on," and "in" more confidently.

Thanks for watching.