The one I use for most of my dishes is the type I get in the Giant grocery stores here in Bluebell, Pennsylvania. (See picture) It is ground chilli with little preservatives added. Use this Sambal Oelek when you want to add heat to your dishes without impacting the overall taste.
Or if you have a lot of time in your hands or don't want the preservatives in your food, you can make your own Sambal Oelek. Please note that this homemade version is quite spicy so use sparingly. Use a glove when handling the ground Oelek.
200 gm small red chillies
1 cup water
1 tsp salt
1 tsp sugar
1 tbsp vinegar
1 tbsp oil
Place the chillies in water in a small pot and simmer for 15 mins. Drain and cool.
Transfer to a food processor. Add the rest of the ingredients and process.
Place in a sealed container and refrigerate after opening.