What are Buffs?

I know it sounds weird but what are they? I'm making a game right now, full of custom spells and I don't understand what a buff is. I'm thinking that its an icon that is put on a certain unit by a certain spell just to show they've been hit by that spell or so a trigger can see that the unit has been hit by a spell. Do buffs accually do anything? I look at them and I see that theres nothing to edit, no stats, nothing. I don't understand the point of them besides showing that the unit has been hit by a spell.

I'm making a spell that slows you but the problem is, is every spell I see adds the buff, "Slowed". Does it accually slow you? Why can't I edit it? I want to know how much this unit is being slowed by.

Anyways, yea please explain to me what a buff is... Thanks.

They give you an icon on the unit and sometimes a pretty little special effect.
That's about it.

They are useful in triggers, because there is some condition that can check for buffs....

See thats what I thought.

Ok here, for example:
Frost Nova, it has a Area of Effect Damage, Specific target Damage, Area of Effect, and that some other things but I don't see anywhere where it says that it slows the enemy. In the Description is says, "Cold damage slows units' movement and attack rate for ## seconds." Now, I'm sure Blizzards not lying so where is this slowing located?

Ah. Slow is a bit different. Slow is not like your usual buffs. I'm not quite sure myself how it works, though I think you can find the amount of slowing in Gameplay Constants. It is most irregular....

Hmm ok.

Well maybe you can help me with this.
I'm making a Custom Spell called, "Frost Grenade".
- I want it to be able to level up the ability to level 3.
- I want it to slow attack speed and movement speed based on level.
- I want it to do damage based on level.
- I want it to be an AOE that you can choose where it hits.
- It doesn't have to be a grenade that hits the ground and rolls. (Even though that would be cool, if you know how to do that maybe you can tell me?)
- I just want it to look like he throws it and it hits an area and damages and slows every enemy within that selected area.

I'm looking for a way to do this but I don't know how. Please help, Thanks.