It is very important to learn to divide words into syllables when learning Lithuanian.

This is how a word can be divided into syllables: žo-dis (word), a-si-las (donkey), lie-tu-vių (of Lithuanians), kal-ba (language), er-zin-ti (to annoy), pirk-ti (to buy), etc.

So a syllable can be made

of one vowel (like a in a-si-las),
of a consonant and a vowel (like žo in žo-dis, si in a-si-las),
of a vowel between consonants (like dis in žo-dis),
of one diphthong (like er in er-zin-ti),
of a diphthong and a consonant (like kal in kal-ba),
of a diphthong between consonants (like pirk in pirk-ti).

As you see, the axis of a syllable is a vowel or a diphthong.

Syllables are vital when understanding diphthongs. What is more, they play a huge role in the Lithuanian stressing system. If you will not be able to divide a word into syllables, you will not learn the stressing. Although stressing is not a thing for beginners, so you shouldn't worry about it right now.