On the surface of your kidneys, millions of nephrons hang out.
Nephrons filter your blood, taking out the stuff you dont want in it to make pee
Take a look at the image:
1. Blood goes in thru afferent arteriole
2. It enters the glomerus which is a capillary network filtering the blood
3. When done filtering, the blood leaves thru the efferent arteriole to go to pertibular capillaries which reabsorb ions and minerals
4. Now, the unfiltered blood stuff goes into Bowman's Capsule thru the proximal convoulted tubule
5. It decends (this part is permeable to water and ions) to the Loop of Henle
6. It acends (permeable to NaCl only) into the distal convulted tubule which drains pee into the collecting duct (the things in here make pee: water urea and bacteria)
(PEI Education Department, 2014)