The first, or 'Root' cakra (aka 'chakra') represents the foundation, not only anatomically, but energetically, as the basis for all manifest events and materials. All things must come from somewhere, something, an innate 'potential' and reserve, and Muladhara represents that 'enfolded' state in the human being.
Within the first cakra, your greatest, highest potential exists. Just as even the smallest atom contains tremendous latent energy, released during nuclear fission, as with the detonation of a nuclear weapon, within Muladhara every human being possesses great power and ability just waiting to be recognized and developed.
On a gross physical level, the Root cakra is located at the lowest of any of the main cakras. For men, it is located just inside (towards the interior) of the perineum (the area between the external genitalia and the anus). For women, it is located just posterior, or behind, the cervix. It is closely associated with the excretory organs (colon, kidneys, bladder).
Muladhara grounds us, as the seat of apana vayu - that 'vital air' that roots us to the earth. It can allow us to feel safe, stimulating awareness that we possess all we need for survival. Or, if out of balance, we may feel panic and a neediness to possess more and more.