By the magic of calculus, we can easily see the relation between force and momentum for a single object. Let's say the a point mass is being acted on by a force . Then we know its acceleration, right? It's just . So what about momemtum? Well if you go into hypnosis you might be able to regress to a time a few weeks ago and then remember the jolting definition of acceleration
Using these two equations, we have
But is just the momentum we've just defined, so when I snap my fingers and wake you up, you'll immediately see that
This is the total net force acting on this one object.
Now let's try to understand two objects.