How to stack runes of same type?

So I have the Enchantress and in the sword tab I have the Vampire Rune and Bounty Rune (I also have a sprint rune). I've read in some strategy guides some suggested runes to use and they mentioned Vampire+Bounty, but I can only equip one at a time?

Same thing for my Bracers.. I have a Retaliation Rune and a Haste Rune but I can only equip one or the other, not both.

What am I doing wrong?

You can only equip one rune per slot: Sword, Helm, Chest, Bracers, and Cape. Fortunately, every single rune is available for every single slot: as you find more runes, you'll eventually get the option to put a Vampire rune on your sword and a Bounty rune on your bracers, or vice versa. If you really want to have lots of life drain, you can eventually have Vampire+Vampire+Vampire+Vampire+Vampire, after you collect the Vampire rune for each slot.

For now, your only option is to find (and then buy) more runes until you have a Vampire (or Bounty) rune in two different slots.