Reading the Pokemon stat pages should give you a rough idea of how stats work.
https://pokemongo.gamepress.gg/pokemon-stats
and
https://pokemongo.gamepress.gg/pokemon-stats-advanced
And yes, higher the defense, the less damage your Pokémon takes. However, please note that Individual Values are not all the stats your Pokémon has. Every Pokémon does have base stats for its species and Individual Values are simply added to those. Technically HP IV is the least valuable for Snorlax because it already has such a high base stamina stat. Attack and defense IV's are proportionally larger compared to stamina. Also, defense stat does come into play also when you dodge. The game first calculates the damage you would take depending on the attacking Pokémon's attack stat, move and defending Pokémon's defense (also, type effectiveness on top of these). Then simply if you dodge, that reduces 75% of that damage you would take without dodging.
