Turkey has a large network of ATMs. As well as withdrawing cash, you can check account balances, pay bills and make transfers. Many banks provide internet banking services (in English) that are accessible 24 hours per day, and also operate telephone banking services (also in English but the quality varies) that offer extended opening hours, right through to a full 24 hour service. To open a bank account in Turkey, you will need to provide proof of your identity and have a Turkish Tax Number.
As with most countries, the tax system in Turkey is complex and bureaucratic and as with most countries, people try to avoid paying tax as much as possible. The Turkish black market is extensive, particularly in the tourist and building sectors where labour is often casual and payments are cash in hand. This explains why the Turkish Treasury relies so heavily on relatively high indirect taxation like VAT to fill the State purse. Having said this, the Authorities take a dim view of those who deliberately flout the law and penalties can be stiff.