Ahri is a burst champion that takes a lot of damage, but she also use alot of mana. Your main damage is the "Q" and the "R".

The "Q" is a skillshot who is good to poke the enemy with.
The "W" give you three fireballs around you and they do damage to the nearest minion or champion.
The "E" is a skillshot who taunt the enemy if you hit them.
The "R" send you slightly forward and throw out a fireball who deals damage to the enemy. You can use the ult three times before it's on cooldown

If the jungler is coming for a gank and you have your ultimate, you have to use your ultimate one time, use your "E", "Q", "W", ult two more time and then you have all your spells on cooldown so you then have to use basic attack if the enemy isent dead. If you dont have ultimate when the our jungler ganks you just need to hit the "E", "Q", "W" and then you have all you abilities on cooldown so then just basic attack.

When you farm in middle lane with Ahri, you just last hit the minions. Only if there is a big wave with minions or you gonna push the lane you have to use abilities to take the minions faster