Sanskrit inherited a system of accentuation from its mother language, Proto-Indo-European, in which the placement of the accent followed certain word-based rules; no general statement concerning accent placement could be made. Yet this accent, which furthermore was not a stress, but a pitch accent (meaning that the accented syllable was higher in tone/pitch than the other syllables) was lost, and the systems described below were generally adapted in its place.
In all English words that are stressed (i.e. that have a syllable which is pronounced more strongly), the stress is clearly audible; yet by looking at the word, you will not be able to predict which of its syllables is stressed: for example, you simply have to know that the word record is stressed on the first syllable (record) when it is a noun, but on the second syllable (record) when it is a verb. In Sanskrit, word stress is predictable, but weaker, and depends on the ‘weight’ (or ‘length’) of the syllables in a word.
LIGHT AND HEAVY SYLLABLES
A syllable always contains a vowel, and usually also consonants before and/or after it. If there is just one consonant between vowels, it counts as standing at the beginning of a syllable: the word भरति bharati ‘he carries’, for example, is thus split up into the syllables bha, ra and ti. When a word contains two or more consonants adjacent to one another (as in the name शकुन्तला Śakuntalā), all but the last consonant are counted as part of the second syllable (Śa-kun-ta-lā). (The same applies to English: think about how you might pronounce and split up words such as woman, fundamental, captain, function etc.)
We distinguish two kinds of syllable: ‘heavy’ and ‘light’ (also referred to as ‘long and ‘short’). A syllable counts as ‘heavy’ when it contains a long or complex vowel (ā ī ū ṝ e ai o au), when its vowel is followed by more than one consonant (and thus it ends in a consonant itself), or when it contains a vowel followed by anusvāra or visarga.