Many Latin students do not get a chance to study iambic meters. For a traditional account of the iambic, you can find lots of information in these online GoogleBooks:
Instead of just two types of elements as in the hexameter (dactyls and spondees), there are five possible forms that an iambic element might take (and, very very rarely, a sixth form). Of these forms, there are two possible two-syllable elements: S-L (iamb, which gives the line its name) and L-L (spondee), and there are three possible three-syllable elements: L-S-S (dactyl), S-S-L (anapest) and S-S-S (tribrach). Very rarely there is a four-syllable element, S-S-S-S (proceleusmaticus), but this is so rare as to not even keep it in mind. If you are curious about how there could be so many possible variations in the elements, check out some of the references above.
So, as the iambic line begins, the element always starts with a decision: are you starting long or short? If the element starts long, you have another decision point: you can now go long (L-L) or short, in which case another short must follow (L-S-S). If the element starts short, you also have a decision point: long (S-L), or short - in which case you have one more decision point: long (S-S-L) or short (S-S-S). So, as each element of the iambic line unfolds, there are two decision points at a minimum, and sometimes three decision points for each element. For various complicated reasons having to do with the underlying rules of the iambic meter (see the references above for the incredibly complex details), the two-syllable elements (L-L, S-L) greatly outnumber the three-syllable elements in any iambic senarius line.
The iambic line sounds complicated, especially compared to the hexameter, but if you think about it as a dance, it's no more complicated than the fox trot, just to take one example! When you do a dance like the fox trot, you might be moving your left foot or your right, and you might be moving that foot forward or back, in or out - there are several many rhythmic decision points in the fox trot, but it's a dance everybody can learn! So, don't worry: once you spend some time reading iambic lines, the five patterns - L-L, L-S-S, S-L, S-S-L, S-S-S - will become just as familiar as the simple two-pattern dactylic hexameter line with its L-L and L-S-S.