This is two simple condiments of Vietnamese cuisine. In the old days, major household do not have refrigerator or freezer, fresh chile peppers are saved and available anytime this way but for some the umami in these chili is favored than fresh chili. They last very long time at room temperature without canning process. In these days, I keep fresh chiles in freezer and only make these in small amount occasionally. They can add a little heat with umami flavor to almost anything from stir fried veggie to grilled meat.
You can use any hot chile pepper, red or green, small or large. Keep the small pepper whole and slice the large pepper as serrano, jalapeno crosswise about 1/16 inch thick.
Put chile pepper into small jars, add a few thinly sliced garlic cloves. Pour enough fish sauce or vinegar to cover pepper and garlic. Do not mix fish sauce with vinegar, only use one kind for each jar. Stir well and press down occasionally, covered and store in the fridge. They will be ready to use but the flavor will be better in 1-2 two days. Check add a little more fish sauce or vinegar to keep chiles covered. Some people can bite directly into the chiles and eat it meal or savory snack. Some use chopsticks or a spoon to smash/cut one into small pieces first and mix with a little pure fine fish sauce or food to diffuse the heat.