Need help stopping spam and using filtering

My email account is practically lost to spam. I've had a little success by choosing the option to "mark as spam" but then I have to take the extra step to move stuff from the spam folder to trash. I've tried setting "filter rules" hoping to move specific items directly to trash, but need some help.

Some specific questions:

How can I set a filter rule using the display name (i.e. USA Wild Seafood) instead of the email address (which changes constantly)?

What is the difference between 'Discard' and 'File into Trash'?

What is the difference between 'Keep' and 'File into Inbox'?

Are the rules case-sensitive?

How/where can I find a list of the rules I've set up? I've set up hundreds at this point but lots of them seem ineffective.

Is there a tutorial somewhere?

Thanks!