1. DUM da = trochaic
Trochee is a metrical foot which consists of two syllables. The first syllable will be emphasized, or stressed (as is the case in the example above - DUM is the first syllable and it is stressed), and the syllable which follows it will be unstressed (as you can see, da is unstressed). Stressed syllables are written in capital letters, and unstressed in lower.
2. da da DUM = anapestic
Anapaest is a metrical foot which consists of three syllables. The first two syllables are unstressed (as you can see in the example above, da da are both unstressed), and they are followed by a stressed syllable (DUM is stressed in the example above).
3. da DUM = iamb
Iamb is a metrical foot which consists of two syllables, like trochee. However, unlike trochee, in iamb, the first syllable is unstressed (da in the example above), and the syllable that follows it is stressed (DUM is emphasized). Shakespeare used iamb in his poems - iambic pentameter.
4. DUM da da = dactylic
Dactyl is a metrical foot which consists of three syllables, like anapest. However, unlike anapest, in dactyl, the first syllable is stressed (DUM in the example above), whereas the following two syllables are unstressed (as you can see, da da are written in lower letters, which means they are unstressed).