Some people dislike the pungent smell of fish sauce. It can be overwhelmingly powerful when tasted on its own, but it's never consumed 'straight'. It's always mixed with other ingredients for use as a dipping sauce or as a seasoning for cooked dishes. The flavour is fishy and salty with an underlying sweetness.
Fish sauce is made by layering fresh fish (usually anchovies) and salt in barrels or vats and leaving it to ferment for several months. It's popular in Thailand, Vietnam, Laos, Cambodia and the Philippines. In general, the lighter, more expensive fish sauces are better quality because they're made from the first extraction; these are usually used to make dipping sauces. Subsequent extractions yield darker fish sauce, often cloudy rather than clear, which is used for cooking.
When buying fish sauce check the ingredients to see it contains only fish and salt. Some commercial fish sauces are flavoured with other ingredients such as garlic and chillies and are meant to be used straight out of the bottle as a dipping sauce. It's easy to make your own and the flavour is better. Mix plain fish sauce with fresh lime juice, sugar, diced garlic and fresh chillies, then dilute the mixture slightly with boiled or bottled still water (water from the tap could cause the sauce to ferment). This is the sauce traditionally served with Vietnamese spring rolls but it's also excellent with fried or grilled fish. You can also spoon this over cooked rice vermicelli topped with grilled meat, roasted peanuts and shredded iceberg lettuce and carrots.
For a traditional Thai salad, shred green mango and bruise it slightly in a mortar and pestle. Pound it with dried shrimps, sliced shallots, roasted peanuts, fresh garlic and Thai chillies, then toss with bottled fish sauce, lime juice, sugar, fresh coriander and mint leaves. If you want to substitute green papaya in place of the green mango, add long beans, cut in 3cm lengths, and halved cherry tomatoes.
Fish sauce is excellent with meat. Mix the bottled fish sauce with pounded fresh lemongrass, lime juice, sugar, garlic, chillies and pepper. Rub this into the meat and let it marinate for several hours before grilling larger pieces of meat (spare ribs and pork neck are especially delicious) or stir-frying thinly sliced meat. You can also use this mixture with shrimp, squid or fish, but only let it marinate for about 10 minutes or the acidity in the lime juice will start to 'cook' the seafood.