The best first food for your baby is breast milk. There are many schools of thought about when solids should be introduced.
Some mothers will introduce solid foods after about four months. One of the reasons for this is that at times your breastfed baby will seem extra-hungry and you may worry that you aren't producing enough milk. And you'll probably be right.
Babies hit growth spurts, and you'll either start some solids or increase your milk supply. I recommend increasing your milk supply.
This is easy to do. Simply put your baby to breast more frequently, and drink more water for a few days. Short and very frequent nursings will send the message that more milk is required and in a day or two, you'll have it.
These growth spurts happen periodically as your breastfed baby gets bigger and needs more sustenance. After that day or two of extra nursings, though, you'll find that you don't have to spend more time with feedings.
Each time you feed your baby there will be a greater amount of milk so you can go back to whatever amount of time with feedings as you did before the spurt.
There will come a time, which varies from one infant to another, when they're ready for more solids. One of my babies let me know at six months that it was time by grabbing a piece of steak off my plate and sucking on it. From then on, while we still continued nursing, I'd also give her mashed vegetables from the family meal.
Her twin, however, cried if I tried to give her solids at that age. It was months later before she was interested in solid foods. Despite the difference in their diets for that few months, they were both alert and healthy.
Another daughter wouldn't put anything solid in her mouth (other than toys or dirt) until she was eleven months old. But her diet of breast milk seemed quite sufficient. She was bright, active, and walking by ten months (yes, she was walking before she was eating solids).
One of my sons decided by six months he wanted solids, and was done nursing on his own by his first birthday.
Introducing solids can be a stressful issue.