What is "Fish Sauce" typically used for?
I grew up with a Vietnamese mother that used to put fish sauce in nearly everything. While I can't exactly recommend all of her uses (she once used it in a texas beef chili -- was not good), there are a few techniques that are good to know.

A common method to create a savory sauce is to use fish sauce with sugar at a 2:1 ratio. For example, you can make Dau phu sot ca chua by sauteeing fried tofu with diced tomatoes and adding 2tbsp of fish sauce to 1tbsp of sugar. This ratio can also be used in stir-fries. I would make sure to turn on your air vents when doing this -- the smell of fish sauce hitting a hot pan is... different than what most people are used to.

It works as a savory salt alternative in a lot of dishes. I use it to season fried rice instead of using salt or soy sauce. It generally is a good idea to add this during the cooking process, so the liquid can reduce and meld with the food.

It can also be used to quick brine ground pork for savory asian dishes. I'd add somewhere in the vicinity of a tbsp per pound of ground pork. I use this technique when making Thai Krapao. There are probably other marinating/brining applications, but I don't have much personal experience with that.

You can also use fish sauce to create a wide variety of dipping sauces -- in general it is paired with something sweet (sugar or rice vinegar) to help balance out the saltiness. It is also commonly watered down (Nuoc cham) in vietnamese dipping sauces to keep it from being too overpowering.

On a personal note, my favorite use is straight up on crispy fried eggs (slightly runny yolk) over white rice. It isn't for everyone, but it's something I've been making and enjoying for years.