Need help understand some stats

What is the difference between cast speed, attack speed and skill speed?

Like what do they influence?

When i have attack speed, using my skills are faster but so is with skill speed so what is the difference?

Increasing attack speed makes the animation of your character attacking go faster and become shorter, which means your character will deal damage sooner after you press your button, and the next attack will happen even sooner because the first attack finished sooner

Cast speed is the same thing only instead of attacks, it's for spells, and spells have a casting animation, like the animation of your character conjuring flames or completing a summoning ritual, instead of swinging his sword. It also goes faster and ends sooner, so the damaging/cursing/etc part of the spell happens sooner.

I'm not sure about skill speed, but I think it means once the skill is activated, it's animation will be faster and shorter. So +20% speed would make a launched fireball fly faster, from 20 miles per hour to 24 miles per hour

Skill is for both. Just hover over the tooltip..it explains exactly that.