To ignore the user, right click a message in your inbox from the person you want to block -> click "Ignore"
You can also auto delete any messages they send (current and future) by doing the following:
Highlight a message that's from the person you want to run the rule on -> On the Ribbon -> Move section -> Rules -> Click Advanced Options... -> in the wizard, check the appropriate selection critiera (most likely "From XXX") -> Next -> Select "delete it" or "permanently delete it" -> Next -> select any additional criteria (optional) -> check "Run this rule now on messages already in "Inbox" -> Finish