Eh depends on susu apa, formula ke susu segar? Kalau formula, follow je instructions kat tin, usually boil water dulu, let it cool sampai 50°C, then mix dengan formula powder mengikut ratio yang diorang suggest (like 1 scoop per 30ml water), then stir sampai larut betul-betul. Jangan guna air yang terlalu panas sebab boleh rosak nutrients, and make sure semua equipment sterilised dulu. Kalau pasal susu segar (fresh milk), just pour into cup and serve je, ada yang nk warm it up sikit especially untuk babies. A few of my mum friends always emphasise timing, once you make formula, kena habis dalam 2 hours kalau room temperature, or simpan dalam fridge and warm again kalau perlu.