I think Taika pretty much said almost everything.

I'd just add a little something really easy to do as a healer to have a small dps contribution at no effort : put your DoT (if your an Astrologian, that's Combust II).
It's an instant cast (so you can use it when running). You'll only have to refresh it every 30s. If you're new and learning, start with only that, that'll be okay.

The rest will come from your experience when you'll gain more self confidence.
Don't listen people to much, a lot are exaggerating because they are frustated. ^^