Does anyone know how the metrical foot works in poems such as iambic tetrameter and such?

I'm not sure what you're asking. A foot is a combination of accented and unaccented syllables. For example, an iamb is a foot consisting of an unaccented syllable followed by an accented syllable.

The meter is the rhythmic structure of a poem; typically, a meter designates the type of foot and the number of feet per line. For example, a poem in iambic tetrameter has four iambs per line, like Anne Bradstreet's "Upon the burning of our house":

In silent night when rest I took,
For sorrow near I did not look

To make it clearer, let's set the feet off in parentheses:
(in SI) (lent NIGHT) (when REST) (i TOOK)
(for SOR) (row NEAR) (i DID) (not LOOK)
In each pair of parentheses is an iambic foot: an unaccented syllable followed by an accented one; and there are four feet in each line.