This article will metion what backend flows are.
Backend flows create an API for you. For instance, you have a Peaka table and are filtering it and doing some actions with flow nodes, and you want to use it your another project. So, you will need to have an API when you create your backend flow. You will get an API and can use it on your projects.
First, you need to create your backend flow. if you don't know how to create it, you can learn it from How to Create a Flow
Then, add your nodes to the backend flow and lastly, click the trigger and then click the 'Copy webhook url' button as you see in the image below.
Congratulations! You can use copied url.