I assume that means more vowel-like letters than words per se - a vav or yud can sometimes be a consonant sound, and sometimes represent a placeholder for a vowel. The closest example in English is the letter Y, which is sometimes a consonant (like in yo-yo) and sometimes a vowel (like in very). In unvowellized Hebrew, the placement of vavs and yuds can tell you where there are oo, oh, and ee sounds. The vav and yud aren’t pronounced - they’re stuck in there for grammatical reasons to show you what the pronunciation would be, and would be carrying the vowels (the cholam, chirik, and um, the oo in the vav one (you memorize the names for these things in kindergarten or first grade, and then they don’t come up again much - I think it’s the shuruk; I can read and write Hebrew, really!)) if you were writing out the vowel symbols. In unvowellized Hebrew, you’ll sometimes write out extra vavs and yuds that you wouldn’t bother with if you were writing out the vowel symbols, as guides to pronunciation.