The human brain is hugely interconnected but three major components can be identified: the cerebrum, the cerebellum and the brain stem.
The brainstem which includes the medulla, the pons and the midbrain, controls breathing, digestion, heart rate and other autonomic processes, as well as connecting the brain with the spinal cord and the rest of the body.
The cerebellum plays an important role in balance, motor control, but is also involved in some cognitive functions such as attention, language, emotional functions (such as regulating fear and pleasure responses) and in the processing of procedural memories.
The cerebrum (or forebrain), which makes up 75% of the brain by volume and 85% by weight, is divided by a large groove, known as the longitudinal fissure, into two distinct hemispheres. The left and right hemispheres ("left" and "right" refer to the owner's point of view, not an outside viewer's) are linked by a large bundle of nerve fibres called the corpus callosum, and also by other smaller connections called commissures.
Most of the important elements of the cerebrum, are split into symmetrical pairs in the left and right hemispheres. Thus, we often speak of the temporal lobes, hippocampi, etc (in the plural), although this website generally follows the convention of speaking of the temporal lobe, hippocampus, etc (in the singular), which should therefore be taken to mean both sides, within both hemispheres. The two hemispheres look similar, but are slightly different in structure and perform different functions. The right hemisphere generally controls the left side of the body, and vice versa, although popular notions that logic, creativity, etc, are restricted to the left or right hemispheres are largely simplistic and unfounded.
Lobes of the cerebral cortex
Picture from Wikipedia (http://en.wikipedia.org/wiki/Human_brain)
The cerebrum is covered by a sheet of neural tissue known as the cerebral cortex (or neocortex), which envelops other brain organs such as the thalamus(which evolved to help relay information from the brain stem and spinal cord to the cerebral cortex) and the hypothalamus and pituitary gland (which control visceral functions, body temperature and behavioural responses such as feeding, drinking, sexual response, aggression and pleasure). The cerebral cortex itself is only 2 - 4 mm thick, and contains six distinct but interconnected layers. It is intricately grooved and folded into the familiar convoluted pattern of folds, or gyri, allowing a large surface area (typically almost 2m2) to fit within the confines of the skull. Consequently, more than two-thirds of the cerebral cortex is buried in the grooves, or sulci.