@민석 김 , I understand you maybe referring to the Azure doc section for the steps - Create a free managed certificate.
You may navigate to Certificates
blade or search for "SSL under your Web App.
(Kindly check the screenshot below)
Also, as mentioned in the doc, ensure that your web app isn't in the F1 or D1 tier, which doesn't support custom TLS/SSL. Having mentioned that, I'll also relay this feedback internally to our Azure content author team for a review, to see if additional clarity in the doc is required.
Thanks for your feedback! Kindly let us know, I'll be more than happy to assist you further.