Why are Syllables important? Well, pronunciation. If you can’t properly divide the word into the correct syllables then you can’t pronounce the word correctly.
Take for example the word marry (as in, to marry someone).
1. ma-rry
2. mar-ry
In the first example the pronunciation is May-re but in the second it is mar-ee, which is correct.
Now, to learn how to find the number of syllables and to count them please head to this site on Syllable Rules (because I can’t summarize the entire thing without copyright issues).