Simple:
* I want to buy a new phone.
* She bought a beautiful dress.
* They buy groceries every week.
More complex:
* Before you buy that car, make sure you get it checked by a mechanic.
* He decided to buy the house even though it was more expensive than he expected.
* The store is having a sale, so I'm going to buy some clothes.
With different meanings:
* The company bought out its competitor. (meaning: acquired)
* He bought time by making excuses. (meaning: gained)
* The argument bought them closer together. (meaning: brought)
Let me know if you'd like more examples or a specific type of sentence!