First you cook the vegetables in the fish sauce, spices (curry, lime, sugar and maybe whatever else you're feeling, experiment!), and the coconut milk. Preferably you only add the thicker part of the coconut milk (don't shake the can) but physics is against you so I would suggest pouring it into a separate bowl first. Then you get the watery part into the bowl and can add the creamy part into the pot (things I didn't do). Cover and cook until the veggies are almost done. Fish cooks quickly so when the vegetables are nearly ready, sample the sauce to adjust your spices (again, things I should have done). Add more curry for more spice and more coconut milk if it's too hot. Add the fish to the mixture and cool until opaque. You can use a variety of fishes but white fish works best.
Once the fish is cooked, serve up some rice and pour the curry over top. It's so delicious!! Now when I make this again, I'll do things differently (aka pay attention to those parentheses I wrote in above). Mine came out a little bland and watery (I told you, I'm white) so I will separate the milk and add more spices to it the next time around. It still looks pretty though!!