Step 1: Heat milk until it becomes little hot. Such that you can dip your fingertip.
Step 2: Now add 1 tsp of old curd to the milk. Stir well.
Step 3: With the help of two containers, mix the milk. i.e. Pour milk from one container to the other. Repeat this step for 2-3 times, such that foam is formed on top of the milk.
Step 4: Now keep it at room temperature or a place which is warm. Like inside an oven (switched off oven :)).
Step 5: After about 8-9 hours, curd is formed. Now you can store this in refrigerator.
