@June ******
When you enter for free (meaning without paying money) is called visa exempt (or visa waiver if you prefer to). Many countries, including the US are elegible for visa exempt. Currently 60 days, it will change to 30 starting Sept. 15th. Visa on arrival (VOA) is a short-term visa available for certain countries, in where you have to fill in a form, paste a passport photo and pay 1,900 (was it 2,100?) baht, and it allows you to stay for a maximum of 15 days. They're different, and in the airport, there's a sign that says "Visa on arrival", that line is for the people that actually need to pay to get a VOA and stay for 15 days. Everybody else, people on visa exempt or people with regular visas can proceed to the normal "big" line. Welcome to Thailand!