In poetry, a "foot" is a measure of syllabic meter and stress that includes two syllables. Let's do as you requested and separate the feet within this excerpt from the poem with bold vertical lines:
Him STILL | must SERVE, | him STILL | oBEY,
And NO- | thing ACT | and NO- | thing SAY,
But WHAT | her HAUGH- | ty LORD | thinks FIT,
Who WITH | the POWER | has ALL | the WIT.
You will also notice that I have placed some words (or parts of words) in all caps while leaving other words without this emphasis. I did this to help you note the pattern of stresses within these four lines. Normally we would "scan" a poem with the use of markings--a small "u" over syllables that are unstressed and an accent or slash ("/") over syllables that are stressed. However, since we are typing this out rather than handwriting the scansion, this is the easiest way to convey the stresses. Unstressed syllables have been left without the capitalization and stressed syllables have been placed in all caps. For example, in the first foot, "him" is unstressed and "still" is stressed.
With these markings in place, it's easy to see the meter of these lines. There are clearly four feet per line (which means it's written in tetrameter-- the prefix "tetra" meaning "four") and each foot contains one unstressed syllable followed by one stressed syllable (which is a pattern known as an "iamb"). Thus, these four lines are written in iambic tetrameter.
The line that most often puzzles students who are trying to scan this poem is the final one we see here: "Who with the power has all the wit." In our contemporary English, "power" would be pronounced with two syllables, which would result in that line actually containing an extra syllable-- a total of nine syllables, which would throw off the established tetrameter. However, "power" is actually pronounced as one stressed syllable within this context: "pow'r." This is a common manipulation that the poet has used to keep her meter intact. We see this technique used again later in the poem when the poet writes, "And all the fawning flatt'rers hate." Don't let it confuse you—this line is still in iambic tetrameter!
This leaves us at our final (and easiest) step: establishing the rhyme scheme. When we look at the final word in each line, it's clear that there's a detectable pattern here. "Obey" rhymes with "say," and "fit" rhymes with "wit." Thus, these lines are occurring in rhymed couplets with a pattern of AABB.