I'm a beginner in the crypto world and I'm interested in purchasing some cryptocurrencies in the United States. Could you please advise me on the best way to do so? I've heard about exchanges, brokerages, and peer-to-peer transactions, but I'm not sure which one suits my needs the best. Could you please elaborate on the pros and cons of each option? Additionally, what are some safety measures I should take to ensure the security of my transactions and investments? Thank you for your help!