How do DNA, enzymes, hormones etc. reach their proper cellular locations?
The answer given by Sadegh gives a general correct broad view. But one part of the puzzle is missing, which is molecular recognition.

Molecules bind to each other via physical/chemical interaction like forming hydrogen bonds, electrostatic interactions and other mechanisms. The sum of all interaction defines the strength of the binding. If molecules have enough interactions, they stick together otherwise not.
Mind that all these interactions have a range of action (a field). Like with magnets, two opposite magnetic poles attract each other at a distance, before they get in contact. Imagine a small molecule getting close to a receptor, if they are "magnetically" compatible they will be attracted toward each other.

Indeed, molecules in the bloodstream (like the Follicle Stimulating Hormone) flow all around the body. However, not all the molecules end up in all the cells. That is because cells have specific receptors on the surface that bind selectively their target. In the case of the Follicle Stimulating Hormone, some cells, like the Sertoli cells or the granulosa cells have the right receptor able to bind that specific hormone.

In the case of a drug targeting the liver, the drug gets assimilated or injected into the bloodstream, it travels all around the body but it is retained by specific molecular interactions only (mostly) in the liver. It is not that the drug knows where the liver is, it is just forced to pass through it and then it is retained by it. The drug passes also through the lungs, but it has no affinity for them so it doesn't get retained.

Inside the cells, it occurs the same. Molecules pass all around, but they do not stick to anything unless a specific protein/receptor/enzyme is found.   

There is an intricate network of interactions both inside and outside the cells, molecules randomly flow throughout this network bouncing on each other until they find the binding partner and they stick to it.

Randomness is not the only factor. Brownian motion occurs, but molecules are also actively moved by different chemo/physical stimuli causing the network of interactions to be in fact extensively regulated.

For example, during the cell cycle, the cytoskeleton is actively remodeled to favor the flow of certain molecules in determinate directions (look metaphase). The cell can also alter its own permeability, actively influencing the influx/efflux of a variety of molecules. 

At the body level, the circulatory system itself forces the flow in a specific direction (from the stomach to the liver for example).

The fact is, that there are mechanisms to selectively control the flow of the molecules at any level in the body, from organs to tissues, to single cells and inside subcompartments of the cells. The topic is complex but very well understood.

I suggest a big dive into this book if you really want to get a grasp on how biological systems work.

UPDATE: As suggested by @WYSIWYG, the picture would be more complete adding a very short note (the topic is way to broad to be extensively discussed here) on chemokines which are a perfect example on how cells can respond to concentration gradients. Chemokines act as a chemoattractant to guide the migration of cells. Cells can sense the concentrations of chemokines in the surrounding environment and, usually, move toward the source of the signal following the increasing concentrations of the signal molecule. In general, it cannot be overstated the importance of chemical gradients during embryogenesis, inflammation and countless other events. Gradients effectively indicate to cells the path to follow.