and always start one food at a time in case they have an allergy. that way you'll know which food caused it. so like bananas for three days, then sweet potatoes.
You can start solids between 4-6 months depending on your pedi recommendation don't start solids with consulting your dr first. They can't have any other milk like cow or goats milk until one year
babies are supposed to have breast milk and/or formula til they are a year. i know somewhere i think around six or so months you can do rice in their bottle and start baby food and stuff like that but newborns and infants eat/drink breast milk or formula. thats it. i think some girls do the rice thing a little early but idk how early.