In Thailand, one of the cheapest places to buy and eat food is by the side of the road. These are the mobile stalls which vendors wheel to their locations every day. Sometimes they might leave the cart there and then bring all their working tools in a pickup truck. Tables are set up on the sidewalk with stools for you to sit on. Quite often these street vendors operate in groups which means if you go to the same place every night, you have a different choice of meal. If there is a group of you, it doesn't really matter if you all order from the same stall or not. Just walk around ordering what you want and then go back to your table to wait. Each vendor will bring you your food. Also, you will sometimes find that one vendor will collect the money on behalf of everyone. The plates are often colour coded so that they know whether you had an ordinary dish (tam-ma-da) or a special dish (pi-set).
If you eat by the side of the road, you will have to know some basic Thai. Not only speaking, but in reading too. Nothing will be in English. There are no menus. Sometimes you will sit first (they might say to you "nung gon" which means sit down). Someone will then come up to you and ask what you want (they might say aow a-rai" which literally means "what do you want" or a bit more polite would be "rap a-rai dee" which literally means "what would you like to receive?" ). If you have already ordered yourself, then just say "sung laew". If not, you just go up to the cart to see what she is cooking. Even if you cannot read Thai, you should be able to work out what she can cook by looking at the ingredients. The cook is usually quite busy so she might not pay you much attention. Just call out what you want. Don't be put off if it looks like she is not listening or didn't hear. Usually she does and can take quite a few different orders at one time.
