How to take good action shots with my Nikon d3100?

I'm a beginner and i know its a good camera for people like me who don't know much about photography. But i'd like to know how i can take an action shot without it being completely blurry… At this point all i can do it use it on auto and even if someone moves the smallest amount its completely blurry. What do i do to make action shots clear?

It depends on what the action is and what direction the subject is moving relative to your camera. For really fast stuff, like cars going 100 MPH, I have found that 1/1, 000-1/1, 250 works pretty well for most off-angle shots. By that, I mean anything where the car is not whizzing by you as you hold the camera stationary. Try using the "S" setting and put your shutter speed at 1/1, 000. You will probably have to adjust the ISO up from 200 to get a decent exposure. On a bright sunny day, though, I find I can get a decent exposure at ISO 200, f/5.6, and 1/1, 250. If there are clouds, I have to bump the ISO up to 500 or maybe higher and I can drop the speed to 1/1000.

For human motion, you will probably make out okay using slower shutter speeds than that, but stick to 1/500 or faster - still using "S" mode for now.

There's a sport mode on the D3100, but I don't know anything about it. Just use "S" and you will be on your way to learning more about exposure with your camera. I usually use "M" so that I can be in complete control, but you're not quite ready for that yet.

If the action is fast, you might want to learn how to use the continuous mode and take 5 or 6 frames that "surround" the peak of the action you are trying to capture. This will increase the chances of getting exactly what you want to capture.

Another thing to learn is called "panning" where you follow the action of the subject with your camera and shoot the picture as you track the subject, sort of like a hunter would follow an animal with his gun before pulling the trigger.

A lot of my action shots are here: Click on the name of the camera over on the right hand side and you will see what settings I used. Maybe this will give you an idea where you need to be for your own action shots.

There's a sports mode on that camera. It's there for people like you, use it!