If gravitons are particles, how is it that they can hold us to the ground, or create gravity between two stars millions of miles away from each other?
Imagine you are sitting a rowing boat on a lake. Stern-to-stern is another boat with an accomplice in it. You are both sitting facing each other (and the stern of your boat). The lake is still, there is no wind. You have a brick on your lap.
You take the brick and gently lob it to your accomplice who catches it. What happens?
By conservation of momentum, the boats drift apart.
Your accomplice lobs the brick back to you, you lob it back to him and so on. The boats accelerate away from each other.
Now, someone on the mountain beside the lake sees the boats but can't see the brick, so to him it looks like an invisible repulsive force is driving the boats apart.
This is how a force, mediated by bosons, works.
To get an attractive force, just replace the brick with a negative momentum particle.
Gravitons work pretty much like that. As to how they can work at great distance; they are stable (so don't decay) and there is nothing stopping them.