I'll give you some examples. For a Pokémon that you want to be a dedicated wall like Vaporeon or Skarmory, you'll generally want to invest 252 HP and 252 (Sp)Def. In some cases you want to go with a mixed set, in which case you'll look up some important benchmarks (avoiding a 2/3HKO from Banded Tyranitar for example) and then take EVs from the first defense and put them into the other defensive stat.
For an offensive, slow Pokémon that you do not wish to invest speed EVs into (and that only attacks on one side of the spectrum), you can again dump it all into HP, or check for something specific that you want to survive and then make your EV spread according to that once more.
You can either end up with some very simple EV spreads (Skarmory with 252 HP 252+ Def or SpDef as an example), or some very advanced ones - from one page back, this is the spread of a Tyranitar:
EVs: 116 HP / 104 Atk / 32 Def / 104 Spd / 140 SAtk / 12 SDef
Naughty Nature (+Atk, -SDef)
So yeah.
It's rarely recommended to invest heavily in (Sp)Def without investing in HP, but there's exceptions (Blissey springs to mind). However, as you're probably new to EVing, I'd recommend sticking to easier spreads for now.