It's basically broken down like this:
1) If it's the Ignore or Forum Mute, they can't see your posts, but you can still see theirs. Just like when someone ignores you, you can still see them, but they're not looking at you or listening.
2) If someone blocks you, those two things hold true, but by blocking you, you're prevented from seeing all of their posts/interactions/etc. However, your posts are hidden from them as well, since it wouldn't be fair for them to block you and then still be able to see your posts.