i would like to use this api in my public app.
Introducing Shopify Subscription APIs: Build Apps That Integrate with Shopify Checkout
if someone know how to use this please help me .
I'd like to use it too, but it's not available yet as stated on the page you linked above.
You can try to get beta access to it by submitting this form (also stated on the link you posted): https://forms.gle/HoWTmeNEcC5TF3sz7