There are many techniques, I like the one where you fold the fabric like you would a fan, you secure the top with a ring or stitches and then fan out the edges straight to make that scallop shape. This shows a paper example
https://www.redtedart.com/paper-fan-...ependence-day/
Or how about something like this, doesn't look so fabric intensive?
https://www.hgtv.com/design/make-and...d-blue-bunting
here's another set of directions but not really any pictures... anyway,
https://homeguides.sfgate.com/make-f...wag-94891.html
PS/Edit: I thought it was really interesting to see all those "pennants" as I would call them referred to as bunting when I was searching, hadn't ever considered them a bunting before.