According to the CDC, it is recommended that you start solids around 6 months old.
Your child can begin eating solid foods at about 6 months old. By the time he or she is 7 or 8 months old, your child can eat a variety of foods from different food groups. These foods include infant cereals, meat or other proteins, fruits, vegetables, grains, yogurts and cheeses, and more.
In the mid 1900s it was common to start children when they were closer to 4 months old, but this is no longer the recommendation.
Please ensure that your baby can sit upright on their own before starting solids—a typical 6 month milestone.
You typically have 2 options when starting solids
It was and sometimes still is recommended that you wait 3-5 days between offering new foods and keeping a journal regarding how your baby interacted with those foods. I, personally, only recommend this if you have a history of allergies.
You will want to give your baby exposure to all types of food to ensure they are getting a variety of textures, vitamins, and nutrients.
Before reading further, please note that your baby's main source of calories and nutrients should come from breast milk or formula. As they approach their first birthday, more of their calories will come from their solid foods and you can reduce formula or breastmilk intake. At one year, an infant's stomach will be able to tolerate cows milk. Formula will not longer be required at this point, but if you choose to continue breastfeeding for the bonding experience, please do.
Baby Led Weaning
If you want to try baby led weaning instead of solids, please read a book on it. I recommend "Baby Led Weaning: The Essential Guide". A book will provide a lot of points that simply can not be summarized into a post such as how to cut the foods and more.
Please also work to introduce peanuts and tree nuts early and often to help reduce the risk of allergies. It is no longer recommended that you wait until a year to introduce these (or any common allergies)