How to transfer from international arrival area to domestic departure area

Clarifying that are referring to IST?

Just follow the signs. You will have lots of company. You will go through immigration and customs. You time is a little tight so don't be afraid to look for a shorter line. Often there will be a line for people with short connections. It would be best to buy your Turkey visa on-line prior to your US departure.

On the same subject : I will be flying from Izmir to US through IST. How much time is necessary for layover in Istanbul ?

IST is a huge, huge airport and last year it had the second-highest number of international passengers passing through it among all the world’s airports. If you want to comfortably make your connecting flight in 2 hours, it’s imperative that you buy your Turkish e-visa online in advance ( use the official government website to buy it @ www.evisa.gov.tr) and book your ticket with the same airline for both legs of the flight. Otherwise, you will need an incalculable amount of time to buy your visa on arrival in a line with many, many other international passengers trying to buy theirs. And— if your luggage is not checked through to your final destination on the same airline—you will be required to walk the longest distance I have ever experienced at an airport to collect it, pass through security yet again, and check the luggage into your final destination. And, unfortunately, that endless walk will need to be done without many moving walkways to speed you along.
Last year, I booked a flight out of LAX with two legs on Turkish Airlines. The first leg landed at IST. The second leg was on a different Turkish Airlines plane going to Izmir (ADB). Turkish Airlines allowed 85 minutes for the transfer at IST airport. Because we all had only carry-on luggage and had bought the e-visa in advance, the timing worked out. It would not have been enough time otherwise.