Assuming you are still on the old email format-------------
From your Inbox page, go to Preferences>>>>>>Email>>>>>>>>Email Filters. Click on that, and then follow the prompts to set up a filter for that sender. One of the options is "Discard", which dumps any emails from that sender and you just never see them.
If you are on the new format, click on the gear icon in the upper right corner of the screen, then on Settings. There you will see Filter Rules. Click on that and follow the prompts.
Your instructions were very clear. I had the new format and did what you said. Unfortunately the person I blocked doesn't email very often so it is too early to tell if it worked but you certainly steered me to where I needed to be on the computer screen. I was unable to find where to do this on my own. Thanks.