This is the biggest mistake people make. The Kurds are not one entity. You can't say Kurds are terrorists or Kurds are fighting ISIS. There are different factions in different countries, taking different actions. They all have different aims. There is the PKK in Turkey, Iraqi Kurdistan(KRG) and YPG in Syria. There are factions Turkey is hostile to and vice versa. People like to confuse that all.

Regarding Turkey, there is the organisation called PKK, which is seen as a terrorist organisation by the US, the EU and NATO. They fight an armed insurgency inside Turkey for autonomy in Turkish cities where Kurds form a majority, since the 80s. Back then, rights for the Kurdish populance was poor which caused this. These cities are located in southeastern Turkey. They are considered a terrorist organisation for action such as suicide bombs, child soldiers, killing teachers, burning down schools, attacking ambulances and the list goes on. Most recently a bomb planted by the PKK killed 6 people including a baby. Currently there is also a big military campaign in southeastern Turkey.

Now to Iraqi Kurdistan. Turkey has good relations with Iraqi Kurdistan and has a base in Mosul, where Turkey even trains a lot of Peshmerga. Economical and political relations are also good. Iraqi Kurdistan is also against the PKK and asks them to leave

And finally there is the YPG. Currently in Syria fighting ISIS to found there own independent country aka Rojava. Turkey is hostile to YPG, sincd they are considered to be affiliated with the PKK.

There is of course a lot more to that, but that is at least the basic info.

Edit: Words, Grammar - all