As with most features on this site, there's more than one way to access your Ignore List. One is through "Your Control Panel"; as lynn P. said, you can click on the "My Profile" link to get to it.
You can also go to the profile of the member whose posts and messages you want to ignore. Under their username (and picture, if any) is a brown menu bar with buttons marked "Send Message" and "User Lists". If you click on the "User Lists" button you'll get a pulldown menu that includes "Add to Ignore List".
Don't be afraid to try it out. It asks you for confirmation, and is just as easily undone.
The other member doesn't get notified that you're ignoring them except when they try to reply to a thread that you've started.
This feature is just meant to help you with your self-care when there are particular members you find triggering.
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