We use the word "buy" in different instances when we want to purchase something or get something through the exchange of money. Here are some examples:
At the store: When you go to the store to buy food, toys, or clothes, you say "I want to buy...". For example, "I want to buy a new video game for my console".
Online: When you buy something online, you say "I'm going to buy...". For example, "I'm going to buy a birthday gift for my friend".
In a restaurant or cafe: When you order food or drinks, the word "buy" is sometimes used. For example, "Can I buy a slice of pizza?".
In a clothing store: When you buy new clothes, you can say "I bought a new pair of jeans" or "I'm buying a new shirt today".
In short, the verb "buy" is used when we talk about shopping - it can be at a store, online or even at a restaurant. This word helps us to express our desire to get something new or needed.