The currency is Thailand is Thai Bath. There are coins 1, 2, 5, 10 Bath and notes of 20, 50, 100, 500 and 1000. See the money
ATM use
The cash machines can be found everywhere. Banks tend to have a few of them in every office, but many 7-11 shops have an ATM outside. There are plenty of ATM's around you, in tourist areas. But sometimes they are difficult to use. Sometimes they show messages in Thai, although you have selected English on he previous screen. In case the machine does something you do not expect, press cancel and go look for another one. Always take the highest possible amount as tre costs are unreasonably high.
Selecting a machine
First look if the machine accepts your card. The Amex, Visa, Mastercard or Maestro logo should be on the machine or on the screen, otherwise this card is not accepted. 
The procedure goes like this:
You enter your card and the first thing the machine asks is you pin code (some machines show a language selector screen before that). Enter your code with caution and cover the keypad with your free hand (as you would do at home).
Sometimes you can the choose English language...
Then you have to press the confirm button. Sometimes this is a button next to the screen where the screen says “confirm”. Sometimes you have to touch the screen, sometimes the confirm is the green confirm button on the keypad. Sometimes, like shown in the picture you have to choose if you want to withdraw Cash. Nobody is at the ATM in Thailand to ask the weather forecast for the next week anyway, but that is not an option :-p
Then you have to choose Current or savings account. Choose “current”.
Then you can choose a fast cash option (preset amounts) or push "key in other amount to enter another amount". Now here comes a tricky part. The maximum amount the machines can give is 20.000 THB. Most machines do not give these huge amounts of money. Just for you to understand, 20.000 THB is a full nett two months pay in Thailand. You can try to get the 20.000... but
If the machines give a funny Thai message (or by coincidence in English “invalid amount”) try again with a lower amount. The machine will warn you that you will get charged a fee of (about) 220 THB (updated June 2017) for the transaction by the Thai bank on top of what you bank will charge you for it. You have to confirm this before the cash will be given. At any point in the procedure you can cancel the procedure by pressing the cancel button on the keypad.
And there comes your money!
ATM use and Maestro
If you want to use the Maestro function outside of the EU, your bank needs to open it for the countries and the duration of your stay. In the past there have been many problems with skimming (illegal copy of the card), so that is why by default this is blocked.
ATM use and Credit cards
Depending on you credit card contract this could be the best option to get money if you have prepaid the amount to your credit card company. Then you only pay the 220THB to the Thai bank and the transaction is free (depending on your CC contract).