Could you be
Fore! You yell, as a ball flies through the sky.
You only say this to prevent any injuries in case a golf ball hits someone (more accurate info can be found here, including the origin of the term). This call demonstrates an act of helping someone by lessening the potential of the golf ball striking them.
Me, you will yell, or somebody could die.
If you suddenly find someone in a state of near death, you would surely yell Help! wouldn't you?
Everyday, in some way, you see me,
Everyday you see an act of help; for example, bees help the survival of plants by collecting their pollen and doing some other fancy works. Every animal species contributes to an ecosystem in one way or another.
Learning to see the forest for the trees.
Deforestation is a terrible thing (ever watched the movie, The Lorax?) and with some help, we are trying to save animals that are losing their habitats via this crime.
It can't be avoided, I'm useful indeed.
Our brains help us to do all sorts of things, so help can't really be avoided, and is thus very useful.
Alive or dead: me, both ways, you need.
Not too sure. We are all dying, quicker and slower than others. We need help?
What am I?