How does those mic under the shirts work?

I have a nikon d5000 that can record video. How and what equipment do i need so that i can be recorded from afar while using a mic under the shirt to pick up the sound

No where in the Specs for that Camera, do I see a MIC jack listed. So if you want to use a Lavaliere type Microphone, your going to have to use a Digital Audio Recorder (DAR) to capture the Audio from a microphone like that.

A Lavaliere Microphone set consists of a small microphone that has a clamp to attach to collars and button holes. It's wire will connect to small, cigarette pack sized device that is a sending unit. This sending unit sends the signal back to receiver, that is plugged into Hydro and also has the Audio feed going to an Audio Mixer, then from Mixer to DAR or just feed the Audio signal into the DAR.

Your DAR can range from something like H4N, small portable recorder, to a cell phone that has recording function available or a laptop, running Audacity, an audio editing and recording program that is a free download.

Generally a lav is clipped to a shirt, on the outside like on a lapel. If the mic is under a shirt you will get a lot of rustling noise and low audio.