A noter, or notary, is often needed whenever you are doing a business transaction or applying for a residence permit in Turkey. For the latter, they are required to notarize your rental contract so you can prove you have a residence. You can find a noter rather easily, since they all have a uniform, white on red sign saying "Noter," with a number in front of it to differentiate them from the other noters in the city.
If you can't find one that way, the Türkiye Noterler Birliği (Turkey Notaries Union) has an official website where you can search for one. Click on Noter Bul (find a notary). That will take you to a page where you can enter the information needed to find one near you.
The option you actually need is İl (province). It is a drop-down list of all provinces in Turkey. Select your province from that and click Araman Başla (start search) to get a detailed list of all noters in your province, by city and number. It will also have the noter's name, address, and telephone number.
If you need a document translated into Turkish, ask the noter. Translation offices with Turkish government certified translators are often located near the noter. If one isn't, the noter will tell you where there office is.
Legalizing a Document with or Without an Apostille
Find a Notary in Turkey: A Turkish website with a smart map, showing the locations of all notaries in Turkey. Make sure you select your province and city/town/district so it will display the notaries near you.
Notarial and Documentary Services Guide for Turkey: For UK citizens, explains these services as provided by the UK embassy and consulates in Turkey.