Well, it does depend on what you can eat - it tends to be spicy.
Meats: Chicken, beef, pork, duck, fish, prawns, tofu.
Veg: usual stirfry types
Spices: chilies, lime leaves, lemongrass, garlic, ginger, galangal(a type of ginger), coriander, thai basil, dry shrimp paste, coconut milk
Starches: rice - usually jasmine, rice noodles, potato (in a few dishes only)
Starters are usually deepfried - like stuffed chicken wings, or egg rolls, meat skewers with peanut sauce, prawn crackers. Mains are usually shared - jasmine rice, Pad Thai - stir-fried flat rice noodles with prawn, egg, beansprouts, chicken (sometimes only 1 meat, but might be a mix) + veg, or curries - not a thick sauce like Indian, but runny, with coconut milk, a chilie + spice paste, stock - with veg + meat.
There are several different curries: green, red, yellow, and one called massaman - it's red and has potato in it. The curries usually have bamboo shoots, veg, beansprouts and meat or tofu, eat with plain rice. Or they will have various stir-fried 'specialty' dishes - and their own version of sweet+sour.
If you dont' know what a dish is, ask.
Soups are big in Thai food as well,a s a starter, but they are all spicy. Tom Yum is the most well- known - hot + sour chicken soup. Great if you've got a cold, will clear your sinuses after 1 sniff!
Everything will be cooked in the dishes, they are usually beautifully garnished with carved carrots, maybe tomato, grated japanese radish (it's white), or shredded raw cabbage. Shouldn't be anything except peanuts - the menu should tell you if there are nuts in the dish, and just ask when you order. Food is eaten with a fork + spoon.
I'd suggest trying a few starters to share among the group - they often have a combo platter. If you only want 1 dish, then pad thai - as it does have everything in 1 dish, or if you can handle spice, then a green thai curry with chicken in it + rice, those are the basic thai dishes as it's your first time.
I love thai food, we have a very good one in the next town over.......... but thai food doesn't like me right now!