Where can you buy Polkadot?

Excuse me, I'm quite interested in the cryptocurrency market, and I've heard quite a lot about Polkadot recently. Could you tell me where exactly I can purchase Polkadot? Are there any specific exchanges or platforms that offer it? Also, is it safe to buy Polkadot online? Are there any risks or things I should be aware of? Additionally, do you have any recommendations on the best time to buy Polkadot, considering the fluctuations in the crypto market? I'm a bit new to this, so any advice you can give would be greatly appreciated. Thank you in advance for your help!