Help using nikon d3100 to take pictures of moving fish?

I've been saving money for this camera for 6 months. Yesterday I finally had enough to buy it.

I've had it for less than 24 hours, haha.

What kind of settings can I put it on to take pictures of my fish in my fishtank?

It focuses great on the ornaments in the tank, but the fish are blurs of color.

How can I get it to focus on the fish?

Is it possible to adjust shutter speed manually? I've found how to adjust aperture, however I do not yet understand the numbers.

You can try focusing manually. Switch the A button to M on the lens.

Unless you take the tank out into the sunlight, it would be hard to get a shutter speed fast enough to freeze the motion of the fish. Electronic flash is fast and intense, so it can freeze motion. However, there's a problem of reflections off the glass if you use direct, on-camera flash. An external flash like the SB700 could help. It will be useful for many indoor scenes. It could be connected with a cord and mounted on a tripod to flash from the side. It can be pointed at a ceiling or wall to create bound flash from above or the side.

It can be done - here is what has worked for me. Wait til you have the most light in the room, tank lights on also. Focus mode: try between 3-D tracking (it tracks and focus on moving objects - kinda) OR Single point AF - where you select the area using the 4 ring outside the ok button. Looking through view finder the area that is red is where the focus will be. Set camera to P adjust ISO to 1600. If using the 18-55mm kit lens don't try to zoom all the way out - you let less light in and shutter speed will slow down. You can always crop the image. You might need to shoot a lot of shots to get the one you are looking for. Hope that helps. Also Ken Rockwell has great website for Nikon gear look him up

Why do noobs like you REFUSE to read the instructions that came with the camera? Of course you can manually change the shutter speed. The entire point of buying a DSLR is to have manual control over the settings. Unless of course you are just another poser who thinks they will get professional looking photos just by using a big black camera…

Read the instrucitons that came with your camera until you understand every single page. Then do what the instructions tell you.