Where do you purchase ETFs?

Can you tell me where exactly one can purchase ETFs? Are there specific platforms or exchanges that cater specifically to ETF trading? Or can I simply use any traditional brokerage account to invest in these financial instruments? Additionally, are there any considerations I should keep in mind before making an ETF purchase, such as fees, liquidity, or tracking error? Understanding these aspects will help me make an informed decision about where and how to invest in ETFs.