Thanks for your question and welcome to the community!
I'm assuming the how to build an Adirondack Chair video was the one hosted by builder Ana White, linked here.
For a step-by-step build, look no further than her own website. She partners with us throughout the year at various Do-it-Yourself Workshops, and I've actually personally met her on one of them while she was here in Atlanta.
On her site, you'll find the how-to build Adirondack Chair guide. Below is an image of it, and you can click here to view the entire post.
Be aware that this write-up didn't have the curved back. However, follow the video's instructions where Ana states that the back can be curved using a jigsaw and making a curved template using a 5 gallon plastic bucket.
Let us know if you have any further questions,