The primary feet used in poetry are:
(NOTE: v = unaccented, ^ = accented)

Iambic: v^
Anapestic: vv^
Trochaic: ^v
Dactylic: ^vv

The substitutive feet are:

Spondaic: ^^
Pyrrhic: vv

The different line lengths are:

One foot: Monometer
Two feet: Dimeter
Three feet: Trimeter
Four feet: Tetrameter
Five feet: Pentameter
Six feet: Hexameter
Seven feet: Heptameter
Eight feet: Octameter

For example:

v   ^        v     ^     v      ^         v      ^         v       ^

“Among all lovely things my Love had been”

-William Wordsworth

This line is in iambic pentameter because it is five iambic (v^) feet.