How can I buy DeFi?

Could you please explain the process of purchasing DeFi tokens in a clear and concise manner? As a beginner in the cryptocurrency world, I'm not entirely sure where to start. Are there any specific exchanges or platforms that specialize in DeFi tokens? What factors should I consider before making a purchase, such as fees, security, and liquidity? Additionally, what are some potential risks associated with investing in DeFi, and how can I mitigate them? Thank you for your guidance.