1.  Exactly where in the kidneys does blood get filtered?

 Within the outer region of each kidney is an area called the cortex.  Here, microscopic structures called renal corpuscles, contain a cluster of capillaries where the blood is filtered.  Fig. 17.4 and 17.5 contain photographs to help understand what this filtering system looks like.  Fig. 17.4 shows how the capillary bundle, called a glomerulus, branches off a small arteriole and then has another small arteriole exiting from it.  Fig. 17.5 is a microscopic view showing a cross-section of these glomeruli within their capsules and renal tubules which carry the filtered fluid away.
 

2.  What gets filtered out of the blood in the renal corpuscle?

 Water, liquid wastes including urea, ions, vitamins, minerals, hormones, digested nutrients (such as glucose, amino acids, glycerol, fatty acids) -- anything in the blood’s plasma small enough to pass through a capillary wall potentially could become part of filtrate -- but only about 20% of the plasma actually does get filtered out.
 

3.  If all those materials could be filtered OUT of the blood, why don’t we become dehydrated, nutritionally starved, and hormone-deprived?

 Because the next step after filtration is reabsorption.  The nephron tubule (see fig. 17.6) is adapted to carry needed filtrate materials out of the tubule into the tissue where it can be picked up by peritubular capillaries.