Nice dude. Apertures are the numbers you see with an 'f' in front of them. Like 'f/4'
Large apertures (smaller the number, bigger the aperture) are used for two main reasons. To create faster shutter speeds (more light entering the lens = less time the sensor needs to gather that light) and to isolate a subject with very shallow depth of field.
Medium Apertures are used for maximum sharpness, with pretty normal depth of field. Best used for images where depth of field isn't a priority at all, like taking a photo of someone against a brick wall? Use f/8 or so.
Small Apertures create massive depth of field, perfect for landscape shots. With such a small opening, a tripod is often used as the shutter speeds become to slow to hand hold. This can be countered with using higher ISO, but the higher the ISO, the more noise occurs in an image.