How to manual focus with Nikon D3000?

I have a Nikon D3000.Im totally new in cameras, i just use cameras like this for taking pictures of my aquariums for online forums and stuff… And sometimes, the auto focus just doesn't cut it. Especially when trying to focus onto little 1/2 cm long fry (new born fish). And i don't know where the thing is to adjust the focus… Please help

Put it in M (manual) mode (the switch on the lens). Then turn the focusing ring. When something is in focus, the focusing light should come on. However, since the object that you're shooting is through the water, this may be tricky. You'd have to use the viewfinder to determine that yourself.