How to buy THETA online?

Good day, fellow investors. I'm curious about how one might navigate the waters of cryptocurrency trading, specifically in relation to purchasing THETA. Could you provide a step-by-step guide on how to buy THETA online? It would be greatly appreciated if you could outline the necessary prerequisites, such as setting up a wallet and finding a reliable exchange platform. Additionally, I'd be interested in any tips or insights you have regarding the security measures one should take while engaging in such transactions. Thank you in advance for your assistance in this matter.