If not, then click on the MANAGE STEAM GUARD ACCOUNT SECURITY button.
Once you’re done verifying your email address, you can turn Steam Guard on. Next, click on the button marked VERIFY EMAIL ADDRESS. If it doesn’t, click on Account from the left side. If your contact information isn’t verified by Steam, you’ll need to verify it before you can set Steam Guard up.
Under your address, you’ll see Status which will show if your email address is verified or not.