How do I start my own contract?

As a cryptocurrency enthusiast and aspiring finance professional, I'm eager to delve deeper into the realm of smart contracts. Could you please elaborate on the steps involved in initiating my own contract? Specifically, I'm interested in understanding the prerequisites, such as which blockchain platform to choose, how to program the contract, and any necessary security considerations. Additionally, I'd appreciate insights into the process of deploying and testing the contract to ensure its functionality and robustness. Your guidance would be invaluable in my journey towards creating my first smart contract.