You want them to concentrate on their starter food for at least 90% of their nutrition at the start because it's a complete food. Opinions vary on when to start introducing other foods. I started by giving mine some chopped hard boiled egg and plain, no fat yogurt at around 2 weeks old. Also, an occasional cricket when I could find one in the yard. Always in small amounts, just to get them used to the idea and to give them something to do.
Once you start offering other foods you'll need to start offering them some chick grit or if you can't find that, some plain parakeet grit (without added calcium) will work.