Why do my portrait pictures come out blurry?

I'm using a Nikon D3100, taking portrait inside with different lighting. I've used the portrait setting, night portrait setting (was told this is good for indoor), and auto. Only three came out clear. Does anyone know what setting or f stops will fix this? I plan on bringing the tripod next time but I know there has to be something on the camera that should fix this.

This is going to be shown in front of many people so I want it to look good.

Added (1). I've already gone through the manual and it does not say.

Added (2). I'm also going to minor in photography.that's why I bought the camera. SLR is a step up from a point and shoot so I'm trying to get used to the settings over the summer.

Without examples, its hard to deduce what your problem is. "Inside with different lighting." doesn't really tell us much. I'm assuming you've got a slow shutter speed because of your automatic settings. Your camera doesn't know what you're shooting, only how much light it sees (and that's not even really accurate). A faster shutter speed should help if this is the case, but you'll need a larger aperture (smaller number) or added light for that.

When it comes to photography, I like to quote BionicDance "Don't run on automatic. Please, think."

"Why do my portrait pictures come out blurry?"

Simple, You are another person who bought a camera thinking that it would make you a photographer and you think that you don't have to learn anything about lighting, exposure etc.

The camera is a tool. To use a tool properly you have to learn how to.
you don't do that by asking "what setting", you do that by reading the manual for a start and then learning photography properly.