Before you get into gear and skills, it’s important to know how basic stats work in this game.
Like all elder scrolls games, this game is based on the holy trinity of Health (warrior), Magicka (Mage) and Stamina (Thief). All abilities cost either Magicka or Stamina, while Health, well… keeps you alive.
There are several secondary stats: weapon and spell damage, weapon and spell critical, resistance to physical or magical damage, and regeneration of magicka, stamina, and health.
All spells that cost Magicka scale with both Magicka and Spell Damage. They crit based on spell critical rating. Light and heavy attacks with staves scale based on magicka and spell damage, and heavy attacks with staves restore magicka.
All spells that cost Stamina scale with both Stamina and Weapon Damage. They crit based on weapon critical rating. Light and heavy attacks with non-staff weapons scale based on stamina and weapon damage, and heavy attacks with these weapons restores stamina.
A critical hit does 50% more damage, although this damage can be increased by various sources such as mundus stones and buffs.
Stamina/Magicka/Health share a pool. You increase these stats by spending attribute points in them (which you get from leveling), through enchantments, and from set bonuses on gear. For the most part, that means that any increase in one of these stats is a trade off with the others. For that reason dps attempt to stack as much as possible into their core stat, keeping just enough in the others to stay alive, as there is no cap on the damage increase you get from your core stat. Tanks, on the other hand, need more health to stay alive, and since their utility spells tend to cost magicka and stamina, they split their points.