Aperture and Shutter Speed go hand in hand they work together to make your picture.
Remember how we said last time that what makes a picture is Light. How much light gets through and how much doesn't. Think of it in units. A picture thats been properly exposed might need 1,000 “units” of light hitting the sensor (if you're using film then its hitting the flim.) All cameras work the same in this moment they can only do one of two things to make sure that those 1,000 units hit the camera.
1:) It can open the shutter for a longer period of time. This is called the shutter speed.
or
2:) It can make the hole at the front of your camera wider (this is your Aperture)

Aperture controls your depth of field or rather how much of your image is in focus and how much is blurry. The wider the aperture the more shallow the depth of field meaning things up close will be in focus but things far away won't. This is best when taking pictures of people or things you want to make the center of attention in a photograph.

See how just the tip of Monster Dog's nose is in focus. This is a shallow depth of field or awide aperture

Now see how everything you see is in focus. From right up close to the camera to far off on the hills. This is a tight aperture or large depth of field. The key to remember when it comes to aperture is that the wider the aperture the more light that is getting through to your sensor which means the faster your shutter speed can be. For shooting inside a wide aperture is going to be your best bet in fact it will be your only choice if you're not using a flash. Aperture works in F' stops. Most camera works through 1 f' stop - 25 f'stops (I say some because some go farther and some go less). How many f' stops you'll be able to get depends on the lens you use, and the shutter speed you're at. The funny thing to remember about aperture is that on a camera the smaller the number the wider the aperture. Meaning f25 would be a very tightly closed aperture opening (or a very large depth of field. everything in focus.)while an aperture of f1.2 would mean a very wide aperture opening.(shallow depth of field. not much in focus.)
I've been told that the best aperture to shoot in to get the cleanest photo is f'8 but this will not work if you are shooting inside or at night time unless you are shooting still life (things that don't move)
the reason being that when you're inside a house or it's late at night your going to need as much light to hit that sensor as possible. To do that you'll need a slower shutter speed, and a wider aperture, but if you're shooting people inside they're going to move around and for that you'll need a faster shutter speed (we'll cover this tomorrow). So to recap:
A wide aperture (lower number) allows more light but shallow depth of field.
A tight sperture (higher number) allows less light but larger depth of field.
When and what aperture field to shoot with will take time and practice....practice often! To start out turn your camera to Priority A (or priority aperture) doing so will allow you to focus on the aperture while the camera worries about the shutter speed. And remember there is no right or wrong there's only what do you like!