We are using Fidelity in this example.
First, you want to go to the Research & Quotes page for your stock. On the page, click on the option chain (representing by the link icon) link as shown below.

On the option chain page, you can select the expiration dates that you are interested in.

On the right side, there are PUT options.

To sell a PUT option, you can click on the Bid price.

You should then be shown a trade popup window where you can provide additional information. Please make sure it is a “Sell To Open” action for entering a trade.
