You can find detailed notes about Latin meter in many online sources. I'm not going to try to duplicate those reference materials here. If you want a traditional account of the dactylic and elegiac meters, you can find lots of information in these online GoogleBooks:
The dactylic hexameter line is made up of six elements. Instead of thinking about the whole line, let's just think about what it feels like as the line unfolds, element by element. In a dactylic hexameter line, there are only two possible forms an element can take: you can have a two-syllable element, L-L (spondee) or you can have a three-syllable element, L-S-S (dactyl). So, for each element, you have just one decision: the element always starts long, and then you have to decide - long or short? If long, you have a L-L element; if short, another short is sure to follow, and you have a L-S-S element. That's it: just one decision point! The element always starts long, then comes a long or short (short-short), and the process repeats again and again, with the final element of the line always scanned L-L.
In an elegiac couplet, the hexameter line is followed by a pentameter line, although that is a bit of a misnomer, since most people do not read the pentameter line as consisting of five feet (for the reading of the pentameter as five feet, see this discussion in Carey). Rather than seeing the pentameter line as five feet, it is easier to think of it as consisting as two halves. In this way of reading the pentamenter line, it starts off just like a hexameter, with L-L (spondee) or L-S-S (dactyl), following by another spondee or dactyl, and then a single indifferent syllable which also coincides with the end of a word. There then follows a second half, which contains a dactyl, then a dactyl, and a final syllable (it is very rare for any spondees to appear in the second half of a pentameter line).