If a camera doesn't have a microphone jack, will it not record audio?

I'm looking at the Nikon D3100 to purchase soon. But I keep reading reviews and seeing the mention of the fact that it doesn't have an external microphone jack. I'm new to DSLRs and photography in general. Does the fact that it doesn't have an external microphone jack mean it won't record audio?

Yes it will record audio but you can't add an extra microphone as it has no external jack.

External mic jacks are added for more serious users, giving them the option of a more professional mic, and one that will be moved away from the camera, possibly avoiding noise of a lens that is auto focusing. Not all dSLRs can auto focus when shooting video however.

dSLRs that don't have mic jacks will record sound with either a mono or stereo mic that's built into the body. No camera maker is going to ship a dSLR that shoots video, that can't record sound.

It has a built-in microphone located under one of those tiny holes in front of the camera. You can just imagine the kind of audio it captures. That's another reason dSLR's were never meant to do video.