Look for the unsweetened kind in the grocery store aisle near the baking supplies. If you can't find shredded coconut, shaved coconut also works quite well. Every cup of coconut will end up translating into two cups of milk. Measure out the coconut into a blender or high-powered food processor. You'll need two cups of water for every cup of coconut you have. Measure out the correct number of cups into a pot. Place the pot on a burner and turn the heat to high. Let the water come to a full boil. Pour it directly into the blender. If your blender is small, you may need to do this in batches. Use a spoon to stir the mixture well. Place the lid on the blender and blend the coconut and water until the mixture is as smooth as possible.  Be sure to hold the lid of the blender tightly in place with one hand, since blending heated substances can cause the lid to fly off unexpectedly. Place a piece of cheesecloth or a fine-mesh strainer over a large bowl. Carefully pour the coconut mixture through the cloth, straining out the solid pieces. The liquid that is left in the bowl is fresh coconut milk. If you're using cheesecloth, pick it up and squeeze out the extra milk before discarding the solid coconut.

TL;DR in Indonesian:
Beli satu kemasan kelapa parut. Masukkan kelapa parut ke blender. Didihkan air. Tuangkan air panas ke dalam blender. Blender kelapa parut tersebut dengan air. Saring hasilnya.