There are 3 main processes in urine formation. These are Filtration, reabsorption and secretion.
Filtration
Blood enters the afferent arteriole and goes to glomerulus where blood is filtered and it will sip inside the glomerulus and nonfilterable components will go into efferent arteriole.
Reabsoprtion
Molecules and ions will be reabsrobed into the system. The fluid will pass into the proximal, distal and convoluted tubules, loop of henle, as water an ions are removed as the fluid osmolarty changes. Last is secretion of substance that is not filtered.