Isn't everything just a bunch of atoms, their position in space, their velocity and their direction of movement?

Just what the title says. I need help.

Edit: I should have given the context from the beginning, but here it is:

I know that is kind of philosophical, but I need to know if what I am thinking makes sense according to physics.

The context is that I am questioning the ability of anything to influence anything. Because if everything can theoretically be described definitely, if every movement of every particle or whatever in the universe is just a result to the movement of another particle, (e. g. collision) then everything could be broken down to the position and velocity of every particle as it was at the beginning of time. And that would mean, for example, that noone can influence anything by their decisions, because their decisions would just be the interaction between the particles in their body. And these interactions would just be the result of how they interacted during the billions of years before. And as I do not have a deep understanding of physics, I need the help of you reditors to prove me wrong. Because in this case I sincerely hope that I am wrong.