The age for variation is officially recommended to be when a baby is 6 months old. In actual fact, the later this is, the more the risk of developing an allergy to a food is reduced as well as the risk of adolescent obesity. However, some foods can be introduced from 4 months onwards (see link below). Bear in mind that breast milk or formula milk must continue to be the main nutritional source for the baby.
It is advised giving food before a bottle. The baby will be more inclined to eat it. As children are naturally drawn to sweet products, start with vegetables. This will enable children to get to know a new taste, "sour".
It is preferable to introduce a vegetable (or fruit) so that the baby can identify the taste and smell. This will also mean that you can see if the baby likes it and check for any reactions or allergies. It is easier to introduce fruit than vegetables, as babies are already familiar with sweet flavours.
Meat and fish can then gradually be combined with vegetables, to provide a more complete meal.