That's basically correct, but let me clarify just a bit. An APRS station runs all the time in normal operation, and can be seen by everybody. There is an emergency code you can set in the encoder, which can raise an additional alert for those people who are watching.

If you have the right equipment, there is a capacity to send short messages. No more than 256 characters, I think. These can be sent as regular email, as long as you are in range of an internet gateway. Winlink over HF really shines for email. I went to Mississippi after Katrina, convoying with another guy who had a new HF Winlink installation. He was able to send and receive email all during the trip.