I don't know how to use my EXT tubes

[AKUK]

Look on eBay for an old 28mm lens. It doesn't have to be Nikon either. Absolutely any make will do. Buy a Nikon reverse adapter to fit the filter size of the 28mm lens (probably 52mm in most cases). Put the tubes on the camera, then the reversed lens with the adapter fitted. You can control the aperture on the lens body. Just be aware with all the tubes attached, the magnification will be pretty extreme and working distances very short. It's mainly for very small objects like ants, jumping spiders or if you wanted to photograph the stamen of a flower etc.

You can probably get a 28mm lens and adapter for about $20-$25 so if money is an issue, this is probably your best bet.