It's really easy to put someone on ignore and it's strongly recommended that you do so with people whose posts you don't like.
Step 1 - log in
Step 2 - click on the "settings" link
Step 3 - click on the "edit ignore list" link on the left side of the screen
Step 4 - type (or paste if you copied and pasted it) the username of the person you want to ignore
Step 5 - click the "ok" button on the right of the screen
One important note though, this won't hide quoted posts. It's an oversight on the developers part and it's not an easy thing to "fix." So if someone quotes someone you have ignored, you'll see the quote.
Alternatively when you click on a person's name and view their profile page, underneath their avatar, there is a option that says, "Ignore this person". Click that link and then click the yes button.