Raiding is a team sport, and knowing your teammates' abilities goes a long way towards a successful night. Instead of griping about why your heals are pitiful compared to someone's or bragging about the meters until people put you on mute, try to understand that each healing class has different tool kits, different strengths, and different weaknesses. With this knowledge, try to mold your own healing so that it works in harmony with your teammates instead of blindly mashing buttons. It can be exhausting to research what each class does, and to put together a battle plan taking those into account on your next fight.
My Guild raids in the 10M format. We don't have the perfect team comp on every fight, but using what I know about different classes helps me flesh out how to best tackle the challenge in front of us. So without further ado, here's a quick and dirty break down of Shaman healing.