How to exchange BTC to ETH?

Could you please elaborate on the process involved in exchanging Bitcoin (BTC) to Ethereum (ETH)? I'm a bit of a novice in the cryptocurrency realm and would appreciate a step-by-step explanation. What platforms or exchanges should I use? Are there any fees associated with the transaction? What's the estimated turnaround time for the conversion? Additionally, are there any security considerations I should be aware of? Your guidance in this matter would be invaluable.