While I was in Thailand, I took a day-long cooking class in Ao Nang. The instructor began by introducing common Thai ingredients like lemongrass, tender garlic, tiny balls of eggplants, galangal, kaffir lime, and kaffir lime leaves, basil, fish sauce, chile peppers, palm sugar, coconut milk, etc.
Thai cooking may seem complex at first with the variety of ingredients used; however, once she explained that Thai cooking is a balance of flavors between salty, spicy, sweet, and acidic, it all made sense — all of these ingredients have their place. One ingredient that I had no familiarity with was galangal, which is in the same family as ginger but has a smoother, more delicate skin. Galangal is tempered ginger with a mild citrus, cedar-like aroma and flavor without the pepper and heat that ginger possesses. Our instructor reiterated a couple of times not to replace galangal with ginger because it will overpower the other flavors in a dish. Kaffir lime leaves were an instant favorite of mine, they brighten curries with an intensely aromatic, fresh lime. (Most Asian groceries carry these ingredients.)
We learned how to make how to make curry pastes from scratch, pulverizing ingredients with a mortar and pestle. While nothing beats a homemade curry, sometimes convenience wins. There are some fine ready-made Thai curry pastes in most groceries. The most common are red and green curries. My personal favorite is the green, which is sweeter, is easier to control the heat and pairs well with coconut milk. I like the Thai Kitchen brand for its high quality of flavor and ingredients and because it's certified gluten-free.
Green curry is a quick stir-fry dish and usually better homemade than take out. Chicken goes really well with green curry, but can be swapped out with shrimp. The fish sauce takes the place of salt and chile paste allows you to control the heat.