Need help staking ETH

As the title says – I need help staking eth. From what I have read, rETH seems to be the best way to do this. But I do not understand where to go to buy it, best/cheapest way to do that, etc. I am somewhat new to crypto currency in general, so if I could get a kind of step by step failsafe guide that would be much appreciated.

I have a couple hundred of ETH on robinhood, but I want to buy a full ETH and steak somewhere. What is the best way to go about this?