How does excretion occur in human beings?

Hint: Excretion is the process of removal of toxic waste from the body of an organism. Excretion in human beings occurs by means of a specific system called the excretory system. The kidney is the main excretory organ that removes the waste from our body.

Complete answer:
Like other animals that have a system to excrete the toxic material out of the body, humans have an excretion system which excretes nitrogen waste as urea, salt and water and is called the human excretion system or urinary system.
This consists of Kidneys, a pair of ureters, urethra and urinary bladder. Kidneys are located in the back of the abdomen and play an important role in homeostasis, that is, they remove waste product from blood, they maintain blood pH and control water content of blood.
Humans have two Kidneys which are located just above the waistline.
The main job of the kidney is to remove waste products from the blood in one day. Kidneys can remove waste products from about 170 litre of blood.
The waste containing blood enters the kidney via renal artery Kidneys contain millions of structural units called nephrons. Furthur nephron contain bowman's capsule, a group of arteries called glomerulus, renal tubule and the collective tube.Waste containing blood enters to the woman capsules where nitrogenous waste are removed from the urine and then passes through renal tubule where useful substances like excess of water and some amino acids are reabsorbed.
The urine then gets collected in a collective tube and urine coming out of the kidney goes to the urinary bladder through a pair of ureters and urine can be stored in the urinary bladder then move out through the urethra.

Note:
For human waste excretion there is excretion system consisting of kidney, pair of ureters and urine bladder from where the nitrogenous waste and other waste from the blood is excreted out in the form of urine moving through the bowman's capsule glomerulus, renal tubule and collective tube and useful substances like excess of water and other ions are reabsorbed.