Helping people with computers... one answer at a time.
Gmail's filters are very powerful, and easy to set up. I'll look at creating a filter to automatically delete email from a specific email address.
I know I can use Gmail filters to automatically mark everything from a specific email address as spam, but I looked at the filter but couldn't figure out how to use it.
Gmail's actually got a pretty powerful filtering utility, however it seems that the one thing you cannot do is set up a filter to automatically mark it as spam. If actually marking it as spam is important, then you'll have to keep doing that manually.
However, a slightly related filter might serve your purposes just as well: "if it's from this email address delete it" is fairly easy filter to create.
Let's start with a message that's in your inbox that's from the sender you want to block:
Click on the More Actions dropdown and you'll see "Filter messages like these":
Click on that and you'll be taken to the filter creation interface, with some values pre-loaded:
As you can see the filter is already pre-loaded with the email address of the sender. Perfect.
Now click Next Step » to indicate what you want done with the message.
Check "Delete it", click Create Filter and from now on you'll no longer see email from that email address - it'll be immediately deleted.
Click on Settings in the upper right of your Gmail window and you'll get the General settings page with this bar of additional settings:
Click on Filters and you'll be taken to a list of filters currently defined for your account, including the one we just created:
Click the edit button and the edit interface we used to create the rule will appear at the top of the page where you can make whatever changes you might like.