Hey,
Urine is produced in the kidneys. Once it is produced, it is carried to the urinary bladder by the ureters. But before the kidneys can actually produce urine and release it into the urinary bladder, blood leading to the kidneys is filtered. Arteries that lead to the kidney are called afferent arterioles. The are called arterioles because this word represents "baby arteries". The blood pressure here is relatively high. Remember, blood contains cells, water, proteins, ions, sugars, amino acids, etc. You don't want to lose all those good stuff, but rather you want to get rid of the toxins found in the blood and excess water (perhaps from drinking too much water). Once in the kindey, the blood goes through this mesh filter called the glomerulus. Since the kidneys is made up of millions of nephrons, each nephron has its own glomerulus. Below is an image of a single glomerulus:
http://www.siumed.edu/~dking2/crr/images/corp5.jpgBelow is an image of a nephron; remember, these things are tiny and there are millions of them:
http://www.cic-caracas.org/departments/science/images/08nephron1.jpgAnyways, the nephron has different sections. According to the image above, the first section is the proximal tubules. Because the glomerulus isn't perfect, if may not do a good job filtering everything at the Bowman's capsule and it may allow things like sugars and proteins to pass through. So, in the nephron, the primary function of the proximal tubule is to reabsorb ions, organic molecules, and water. This process is called reabsorption and there are four main steps in urine formation, with reabsorption being one of them. What ever is left after this original section goes into the loop of Henle (that long part that looks like a large loop). In other words, it's the hairpin-shaped segment of the nephron. Here, more water and ions (such as sodium and chloride) is reabsorbed into blood vessels that surround the loop. This can be done through either active transport or passive transport - depending on what's being reabsorbed.
Next, urine moves through the distal tubule, the last segment of the nephron, and finally into the collecting ducts. As the name suggests, the collecting ducts collect urine from the million nephrons that, in turn, merge in the pelvis of the kidney and flow into the ureters, which in turn lead to the bladder.