What is the difference between 1st foods and 2nd foods does it matter when you start the baby on 2nd

Straining. Both are pureed. Step 1 foods are then strained to remove any high fiber material. Reallistically by 6 months most kids are ready for step 2 foods.
Items in the food. First foods are generally composed of components of a single item, like green beans, with not fillers. First foods help you identify food reactions like vomiting, diarrhea & rashes. If no problems show in 0-4 days, the item is a "safe" food. Second foods will have components of 2 foods. Feed more than 1 new thing at a time & you won't know what caused the rxn. I've hospitalized several with rxns.